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Which battery to purchase:  Lead-acid AGM? VRLA? Flooded?
What about Lithium batteries? 
Differences.  Recommendations.
Filling a new 'flooded' battery & initializing it properly.
Peculiarities of various types of batteries.
Rejuvenating and rejuvenation service.  LOAD-TESTING.
Chargers (SMART ....and not).
Maintenance voltages ....and other information.

This is a long article.  It covers vastly more than you probably ever thought you wanted to know.
This article purposely includes nearly everything about batteries for vehicles.
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Copyright 2023, R. Fleischer


You may want to read this now or later:   The article has some information on batteries that is not in the below article.

Vehicle batteries are no longer only the simple flooded (slosh) batteries of my youth.  There are now many choices.  More choices will be seen in the future.   No longer can a complete article, like this one is attempting to be, be relatively simple.  There is a lot to know about battery chemistry, usage, purchase, maintenance, etc.  Don't worry if you get confused will get plenty of information that will 'stick with you' ...and you can always re-read this article.

The longest lasting batteries are still, over-all, ...taking into account all variables, ...the flooded (wet, slosh, lead-acid) types, in a quality brand. You can expect reliability in motorcycle usage, if the battery is not seriously abused, for 5 years, but increasingly less reliable as 8 years approaches.

The second longest-lasting batteries (compared to high quality sealed slosh batteries) are likely the sealed or semi-sealed slosh/flooded lead-acid types, which are likely very close-to, or might even have the same reliability, as the flooded types.  Properly taken care of, you can expect reliability for 5 to 8 years from these various types.  The Odyssey, or other sealed battery have the potential to be the longest lasting, but there are reasons why I have not included it into the topmost level.

My use of expected life numbers in this article means that you can probably expect the battery to reliably start your bike in any weather condition as it ages to my stated life guesstimates (except perhaps below 0C).  With reasonable care, the battery should retain a reasonably usable capacity, typically over 50% of rated AH, over its expected life.  After my noted expected lifetime, you can expect rapidly decreasing reliability.  It is because of the lowering of reliability that I have made my conservative recommendations for scheduled battery replacement.  My stated life for batteries is based on load testing the battery regularly, using the load testing method I describe.  Keep in mind that your results may be quite different; my figures are based on reasonable care, reasonable use, and having an average-to-better-quality battery.

Generally, very good reliability is had with the AGM/VRLA batteries, with the Panasonic and Odyssey being two of the very best.  I do not mean 'a copy' of the Panasonic. Panasonic and Odyssey batteries are ruggedly built and can be normally expected to last at least 5 to 8 years, some go considerably longer.   It is possible for these batteries to exceed the life of flooded/slosh batteries, if these batteries are well-taken-care-of.  One reason that AGM/VRLA batteries may not have lifetimes that exceed flooded (slosh) batteries is due to heating by our motorcycle engines which can affect these very tightly packaged batteries, combined with vibration and fast charging which can cause spot heating effects.  A premium AGM/VRLA is likely to last a long time, given reasonable care, and this is particularly so if the battery is in a steel case (few ever purchase them steel case enclosed).  Your own usage, and that includes a long list of things, makes, on average, a lot of difference in battery life.   Averages are just that; and some batteries will greatly outlast others, even in the same brand and relatively same usage; while others will have shorter lives.   There is also the fact that in any brand, reliability can vary; and you may be ....unfortunately,  ....the one who gets a poorly built or other problem battery.

There are numerous factors affecting battery life, and they include (but are NOT exclusive-to) how long the cranking periods are (how much cranking you do before the engine starts), the temperature at which the battery is used at, how often the battery is considerably discharged (and for how long it is so-discharged); and, the condition of the starter motor and somewhat on the thickness (viscosity) of the engine oil, higher compression ratios of certain engines, etc.

Batteries (some especially so) are sensitive to the rate of charging, particularly when they are hot from exposure to engine heat, and there is some good evidence that large oversize alternators can have life-shortening effects on the battery under some situations.  The use of high power alternator systems can be hard on a battery, particularly if the battery is allowed to discharge considerably, because the re-charging current can be quite considerable, which creates heat, sometimes small spot heat, inside the battery.   Small spot heating can injure an area considerably. The stock alternator on the /6 and later is capable of a considerable charging current, and moreso many aftermarket alternators.   There is also a somewhat nerdy thing about inter-cell-connectors corrosion and the already mentioned large recharging currents.

When I list the average or expected life here, I really do mean average/expected solidly-useful life; that means under a variety of conditions.  You might get less ...or more.  Keep in mind what average is, mathematically.  If properly taken care of, both the Panasonic and the Odyssey, brands often talked about, are usually very good batteries; but, like ANY type of battery, one should pay attention to charging voltage/current & especially avoid excessive discharge for any period of time.    The genuine Panasonic battery may not be as sensitive to being heavily discharged for the short term, compared to many other types.  Average life can follow a Bell-Curve, or a badly misshapen curve, with a steep drop-off from, let's say, the midpoint of life.

There are so many variables that it is difficult to provide owners/riders with accurate statements that are applicable to others, or to say that one battery is always vastly better than another.  I did a lot of testing and gathering of information over many years, and still do some testing (I have sophisticated testing equipment, and I also did cold weather testing of various types).

Of lesser life and reliability, are the cheaper flooded, AGM and some gel types.  True gel types particularly do not like quite high charging rates, and are easily damaged by being overcharged.

BMW has sold a battery they called a Gel type, which may be equal to the Panasonic in life expectancy, provided it is "properly taken care of", which really applies to all batteries.  Gel batteries are not as good as non-gel, at low temperatures.  If you tend to start and operate your motorcycle in the Winter, with temperatures near or below freezing, where battery demands are high, the GEL type would not be recommended by me, particularly over the long term.   I put Lithium batteries in this same category; that is, they are not very good at low temperatures ....but the Gel types can be even worse, and have a tendency to fail without advance notice.  While this is not unknown for all battery types, the Gel types are more prominent in this.

The LiFePO4 (ONLY!) type of Lithium battery ...could theoretically have the longest life, but has to be treated quite correctly, as there are some serious problems and variables ...and if not treated carefully the life expectancy could be quite low; especially the LiFePO4 batteries that have no built-in battery maintenance circuitry, which prevents over charging and excessive draining too; ....of course, you may be lucky.

If any type of battery is not taken care of, its life expectancy will be lower.  I have seen quite a few high quality batteries that lasted less than one season ...due to neglect.  If you are the type of person who does take care of your battery, you can possibly get as much as 50% longer life than my averages, but you probably will only get 20% additional life.  50% longer would be quite unusual; especially in colder climates (where you actually start and ride the motorcycle).  This is because motorcycle batteries are located in a poor environment for best longevity, such as heat/cold/vibration ...& poor re-charging.

Below is a discussion of Lithium batteries ...>>>>immediately afterwards are all the other types of batteries and information.

LITHIUM batteries:

I do not recommend the Shorai & other common Lithium type batteries for street touring use. I have not tested any in-great-depth, because other folks have, and their testing seems to be well-done:

The LiFePO4 type, only!! ... is being discussed here ... as all other lithium types should not be used at all, due to possibility of fires.
NOTE!   Early versions of lithium batteries often, if not usually or mostly, did not contain protective circuitry, to protect against over-charging; and, to protect against excessive discharge.  Lithium iron phosphate batteries can be ruined by excessive discharging. The better, and later models of LiFePO4 batteries, for motorcycles, now almost always contain protective circuits.  BE SURE to inquire about that, if purchasing a lithium battery!

In my opinion the old style Lithium battery being sold for motorcycles should be used only for racing, where the weight decrease and/or small size and low AH rating are worthy or otherwise acceptable.  You might also consider them for a Caf bike.  There are problems with these batteries with capacity ....and if voltage gets too low (no protective circuitry in the battery) or the temperature is near freezing; .... or if charging is improper, and certain other details, all of which I will set down in this section of this article.    The batteries do NOT have high ampere-hour ratings like the lead-acid types. On the other hand, they have lengthy shelf-lives, and can provide a large ampere-flow (if for shorter time), and, have a slightly higher voltage (around 13.3)..thus, may crank your engine very smartly, indeed.

A major problem will be seen if the actual AH (ampere-hours) of the particular lithium battery is too small for YOUR needs; and/or, if the lithium battery gets quite heavily discharged, because there was no BMS (battery maintenance system) built into the battery.

There is a serious need for watching the charging process; ...particularly if using a Smart Charger that has a de-sulfation mode (charges to a rather high voltage for short periods or uses sharp voltage spikes).  I highly recommend you do not EVER use such a mode on a lithium battery.  Another problem occurs if the Smart Charger is a type that too soon reduces the charging level, & in particular if the very heavily discharged battery is charged too quickly ...and some other considerations. LiFePO4 vehicle batteries are considered fully charged at 13.6 volts; & should not be charged to too high a voltage.  14.4 seems a good practical limit, although some literature might allow 14.6.  Never exceed 14.6 volts will permanently damage the battery, even if overcharged briefly.  14.6 volts is lower than allowable for other types of batteries, which generally have a limit of ~14.9.   

Many lithium vehicle batteries are now available that have the mentioned internal electronics that are more protective and some slightly higher voltages, etc., may be allowable.  Read the seller's and makers literature, and if the information is not there, ask for specifics, and print them for yourself

Lithium batteries can be permanently damaged by being discharged too much, even once, although that damage need not be fatal (but can be).   Some brands now have internal protection against excessive discharge.  Lithium batteries are different from lead-acid batteries in this respect ...a lead-acid battery can be fully discharged, even to zero volts, & if not heavily discharged for too long a period of time, is likely recoverable; this is especially so for old-fashioned flooded batteries.  The big thing with lithium batteries with respect to being heavily discharged, if such is possible, is that re-charging SHOULD BE started at a very exceptionally low rate!   Many specialized chargers designed for these lithium batteries have special recovery modes, if the battery gets seriously drained.   Nearly all lithium batteries that are sold for bikes, do not have internal control circuitry to totally and completely "equalize" the cells.  However, this can be 'acceptable'.

Some of the newer lithium chargers (see the manufacturer of your proposed battery, such as Shorai) have fully-controlled chargers now available ...I had been expecting that to happen.  Chargers for lithium batteries are special, or should be, but need not absolutely have to be, but use with common Smart Chargers will take some smarts on your part.  The most expensive lithium batteries, and possibly some few bike types, have electronics assigned to each and every cell separately, to ensure equality of charging; holding charging currents & voltages to a tight specifications.   Since the cells of all batteries you will be using on your engine-powered motorcycles and cars, are in series connection, variation between the cells will cause an unbalance in voltage on any particular cell....and the moreso, the harder it is on the battery.  This can be a problem with many lithium batteries I am discussing in this section of this article.

You do not have to purchase a special charger; ...but you should be extra careful using non-special chargers.  I generally recommend special chargers for lithium batteries.  Truly purposeful lithium battery chargers control the voltage, not just current, for the battery charging when the battery is highly discharged, and more tightly regulate the maximum voltage.  These things are very much not understood by most.  Remember:  You have $$$ invested in that lithium battery; and, you want it to remain reliable.  If your lithium battery has built-in protection, you are far better off, and likely won't need a special charger.  Just do not use one with the high voltage spike output that is for rejuvenation of lead-acid batteries.

Lithium batteries can be extremely expensive in equal AH sizes; and, most cheaper or early types are easy to seriously damage from being discharged, require special charging ...and have other problems ...depending on circumstances.   Racers and caf riders may use them.  They will hold-up with some abuse, but not a lot of abuse.  These are not the type of battery you want if you like to use your electrical system considerably when the engine is off.  Similarly, they are not the type of battery you want if you expect to reliably start your bike in freezing conditions, as power output of these batteries falls off very fast when they are cold; and, bike batteries of the lithium type have very low true ampere-hours (AH) ratings.  You can TRY turning on the headlight as a 'load' for a few minutes, before cranking. There are quite a few street riders now using these batteries. Just because some have good luck with them, does not mean you will.  Consider very carefully how your battery will be used, and under what conditions, etc.   These lithium batteries are pricey even in their typical small AH sizes. 

Lithium batteries have a very flat voltage discharge curve.  On a practical basis, that means they work fine as they discharge, and then, with no or very little notice, will suddenly go completely dead ...and; if not protected internally, likely will be seriously damaged when recharged by such as your bike's alternator; or, a common charger.  That might not happen if it is then re-charged at a very low voltage to begin with. This is quite different from other batteries, in which a light to modest recharging current (amperes) is appropriate the beginning.  I suggest you re-read this paragraph.

If you do decide to get a Lithium battery:
Be sure it is the LiFePO4 type. This stands for Lithium-Iron-Phosphate.  This type of battery is much safer than the Lithium-Cobalt type.  The LiFePO4 type is much more thermally stable & it does not have the thermal-runaway problems of the Lithium Cobalt types which can lead to a fire!

When using a LiFePo4 type battery, be sure that its real ampere-hour (AH) rating is sufficient for you not get one too small in real ampere-hour rating.  While it may start your engine in decent weather, when it is cold the battery output is lower (this is common to all types of batteries, although the effect varies) and if you have heated clothing and other loads, you may run the battery down very quickly, especially if the charging system is not working strongly, at, say, idle or just above idle. Watch out for 'equivalent to' ratings... xx AH ...Ampere that is MEANINGLESS!  If the battery is rated in "lead equivalent", this is another wishy-washy half-assed way of specifying the battery.  If the battery is too small in REAL AH rating, then it could be discharged from such as the headlight, etc.,  especially in very slow going where your charging system has a low output.

A lesser problem, usually, is that the battery could be overwhelmed by powerful aftermarket charging systems. This is moreso for lithium batteries when the battery is considerably discharged.   Many do not consider the charging rate possible from a motorcycle alternator, particularly the aftermarket larger ones, but even the stock Bosch 280 watt alternator can produce 20 amperes, of which as much as 14 might be available for re-charging, such as with the headlight off.  An alternator rated at 450 watts, less normal bike loads, might have 375 (or bit more) watts available for your battery. That is over 25 amperes. Will the battery accept that amount of short-term charging rate without damage?  There is even a 600 watt aftermarket alternator now.

Many lithium batteries have their real AH specification well-hidden in the literature, if you can find it at all.  There may be a sticker on the bottom of the battery. Some of the sellers do not mention that if the battery is well-discharged, a sudden fast charging will destroy the battery; or, at least reduce greatly its otherwise expected life.  Some makers/sellers literature rate their batteries in watts ...tricky to properly understand, and not informative. This is the same for 'lead equivalent' ratings.    I recommend you do not purchase a lithium battery that is rated at 6AH (approximately) in actual capacity, as you can discharge it much too easily ...but, this is up to you and your needs in your real world usage.  Lithium battery ratings are often stated in a way that may make you think the seller/maker is comparing the battery to a lead-acid battery.  Be cautious!  You will likely find that a Lithium-Iron-Phosphate battery of even half the true AH rating of the common Airhead-sizes of lead-acid batteries is very pricey...and probably not available at all in a physical size that will fit your bike.

So, what's with this stuff about AH (ampere-hour) ratings?
Any battery must not only deliver plentiful cranking amperes at any temperature you will try to start the bike at; but, the battery must deliver low levels of current for long periods of time ...much longer than the short term high output level needed when cranking the engine.  If you have to do a lot of cranking, especially if you ride in quite cold temperatures, and/or if you have lots of current-draining electrical goodies, or do a lot of stop and go riding, you could discharge the battery enough to not be able to start the engine. This damages any battery, but can seriously damage or ruin a lithium battery if it is not internally protected against too much discharging; and very few cheaper ones are so protected.  If you have heated clothing, heated bars, gloves, vest, .....those draw current, sometimes substantial current.  It is worse if you have a larger wattage headlight or powerful auxiliary lighting. Especially bad with lithium batteries is if you use the headlight during setting up a campsite; or use the battery to run accessories (that may be off-the-bike types ...maybe a lamp on a cord, CPAP, etc.).

Consider what a true 6AH lithium battery specification really means during cranking and other usage.  Even if the battery was capable of delivering the full 6 AH capacity at quite high drain levels, which it is not, let us assume here that it is capable of 6 AH at any drain level amount, to give the best possible rating for that battery ...and make calculations easy.

At room temperature approximately, a good LiFePO4 battery can deliver a quite large number of amperes.  Unfortunately, when the battery is near the temperature at which water freezes, the battery's capable output substantially decreases.   On a freezing morning with a cold engine, your Airhead may need 200 amperes of current for your starter motor to even begin rotating the engine, and could need 100+ amperes to continue rotating.   If the engine started fairly quickly/easily, there is likely not going to be a problem, unless the bike sits at idle for a long period of time, has some added powerful lights, heated clothing, battery has been drained some (see above paragraphs)...etc., all of which plus ignition and whatever else is turned on, is draining the battery.  If it is cold, things can get marginal very quickly.  Battery charge tends to decrease in stop and go traffic, in some circumstances this can happen rather quickly.   The storage or available capacity of that lithium battery (6 AH being assumed here), assuming no other large drains than just to start the engine, and means that you could crank, for a bit of time, each, quite a number of times ...allowing the starter to cool off between starting attempts (the way you really should use a starter).    You may be thinking that there isn't any problem for you...well, maybe you have enough battery capacity?  Really?

Let us say the starter did draw a fair amount in starting your bike...which is fairly common.  For a common lithium battery you have used-up a fair amount of the battery's 6 AH capacity for cranking.  On a practical basis, it will be considerably worse in cold weather.   That should, ideally, leave plenty for some idling time, then you can ride down the highway & hopefully the ride is long enough at a decent RPM to replenish the battery.  If you make a number of stop & go's, particularly short, say in busy traffic cities or traffic-backed-up freeway jams; maybe have more lighting & heated clothing; if the battery is not being recharged enough, ......the battery may not have enough charge to start your bike again. There is only so much total battery capacity.  AGM, VRLA, and flooded batteries, that are in common sizes for the Airheads, all have very much higher AH storage capacity (the Lithium batteries sold for motorcycles typically have very much lower AH ratings) a more conventional battery will give you a very much larger 'safety factor'.   This extra safety factor of conventional flooded, gel, & AGM/VRLA batteries will be as much as 5 to 7 times on the larger BMW Airheads motorcycle battery sizes, and as much as 3 to 4 times on the smaller battery size, all in common use on Airheads. 

Thus, while a true 6 AH battery might work OK for you, it might not.  Consider what the situation would be if you had a regular lead-acid battery, rated at 28 AH ...and changed it to a 6 AH.  You lost a high percentage of the stock battery capacity.  This is what purchasing the common lower AH lithium batteries will do.....and, see the next few paragraphs.  Another problem is that the Lithium battery has a very quick and very sudden cutting-off of output....this is commonly described as a very steep discharge curve.  There is VERY MUCH LESS WARNING that the battery is discharging and nearly dead.

The 6 AH lithium battery will run the engine, lighting, etc., for far less time, if you had any situations; or combinations, such as an alternator system failure or marginal operation, used the battery at a campsite, did a lot of stop and go ...had heated clothing, large headlight ...and many other situations.  There are good reasons BMW selected a certain battery size (in ampere-hours) for your bike; many factors were considered.   Consider what having a stock 28 AH battery means to you, if your alternator fails, and you are riding at night, maybe it is raining, and you are in the middle of nowhere.  Turning off the headlight or changing to the parking light position, or, whatever you can do to reduce the headlight's amperes drain, is very likely enough, with a lead-acid battery, to allow for HOURS of riding, with a dead alternator.  NOT SO a 6AH lithium battery! could less than an hour.

It could be that a small capacity battery is OK for you for all your starting and riding conditions. Maybe.

Many LiFePO4 batteries, if discharged enough, can be seriously damaged.  4 "cells" are used in a "12 volt system" in this type of battery. If the terminal voltage should fall below 2.5 volts per cell (10.0 volts at the battery terminals), the battery is being damaged.  Serious damage occurs below 8 volts.  So, make sure you never let the battery become discharged to or below 10.0 volts.  In addition, be aware that many Smart Chargers (that includes the Battery Tenders) may reduce their charging level too soon for the LiFePO4 batteries, if these batteries were fairly well discharged to begin with.  Mind what I said earlier about not re-charging a heavily discharged lithium battery initially at anything but a very low rate (and, that means voltage and current).  Guess what happens if you try to start your motorcycle with a jumpered-battery, perhaps from another bike or a car, and you have a lithium battery..?   DAMAGE, & it can be bad and expensive.

The stock charging system in the Airheads will work OK with a lithium battery (if it is not heavily discharged), but a small increase in charging voltage is appropriate ...just as it is for even the stock flooded battery, or any AGM/VRLA, because BMW set its stock voltage regulators fairly low, often found to be approximately 13.8 volts as measured at the battery itself.  That is not enough to quickly or even moderately quickly, recharge any battery from such as cranking, sitting at traffic signals, stop and go, etc., but on a flooded battery, water use is lessened with the lower voltage.   A much better compromise is 14.2 to 14.4 volts, which covers all conditions of usage reasonably well, and takes into account lamps life, battery types, etc.   I think that if you install a lithium battery, you should adjust the voltage regulator higher, and follow the lithium battery seller's recommendations, which may be slightly higher than 14.4.

The lithium battery has other characteristics that differ from lead-acid batteries.  Just one such is that after a complete and full charging (assuming the charging is to proper high-enough voltage), lithium batteries will have a resting voltage (after several hours for example) that is a bit higher than you are used to seeing, 12.8 or even slightly higher.  This resting voltage does not change very much as a light to moderate load is applied.

While there are some good things about LiFePO4 batteries, these are notable:
LiFePO4 batteries are generally capable of more life-cycles (in practice, that usually means how many starts over the years you get before the battery fails or starts to fail).  They can be charged faster than common lead-acid batteries ...that is ....they will accept a faster charge without damage BUT....ONLY IF they are not already heavily discharged.  They do not have Peukert's losses ...the main article below gets slightly into Peukert's.   They also don't waste hardly any of the charging power in charging efficiency losses, which can mean faster recharging.

If your Lithium battery was discharged to nearly dead, the voltage being, perhaps, near or close to zero under a load; you really should begin charging at a fraction of one volt.  I did not say amp, but volt! You are unlikely to have the equipment to do that.  A deeply discharged lithium battery must be recharged at a very low rate of both voltage and current, to gain back its full potential (pun).
I recommend that for lithium batteries you do not use a constantly-on and connected Smart Charger, as this will slowly damage them ...and the damage accelerates over time.   I suggest you charge the battery fully, then set it aside, with no load.   If the battery is left connected to the motorcycle system, the drain of the motorcycle (clock, etc.) in not-running mode is going to discharge the battery some, so I suggest you recharge the battery now and then.  If the drain is excessive, or you want to eliminate it, simply disconnect the battery after charging, store it, and once a year or so re-charge it.

There is some evidence to show that using Smart Chargers continuously with any type of battery will adversely affect battery life.

Best is to use a quality charger that is specifically designed for your lithium battery.

Unless it is an emergency, never, ever, jump start a bike with a highly discharged lithium battery.  This is effectively the same as hugely excessively recharging the lithium battery ...and it may ruin the battery immediately; where, before, you might have had a chance at recovery. A somewhat less damaging situation is to bump start the bike if some battery charge is left to allow this, and hopefully you do not have a hugely oversize alternator.

NOTE what I said earlier about LiFePO4  batteries that have internal electronics for various protections ...but they are hard to find and usually extra costly, and, they may give zero warning of suddenly dying charge.

Am I totally against LiFePO4 batteries?! ...not at all.  I simply want you to know what you are getting into.  Anyplace I'd recommend them?  Yes: racing & and minimalist caf bikes in particular ....and a "maybe-maybe" for street riders who do not need the larger capacity of stock batteries and are willing to properly maintain and use the battery.

Rejuvenating lithium batteries electrically, assuming the battery is very heavily discharged:

A special charger is a must for the best results.  Yes, you could use some other methods, but you would need to carefully control the regulated voltage and regulated current output.  I have successfully done that in my own shop on lithium batteries that were completely dead, but I have specialized equipment with which I can control the battery input and source outputs quite precisely.   It is a MUST to start with a quite low voltage and low current, and a regulated, controlled, power source is the best...see earlier, ...and later this article about lithium batteries.

Methods that are safe and cheap (but have only a maybe 60% success) will be described here, since most of you can do these methods.  I will also, in a red box, tell you about my method, that has a much higher success rate.

You need a non-smart battery charger, often called a Trickle Charger, that, except for its output wires/plug, simply entirely plugs into your wall power socket.  A rating of ~0.25 to 2 amperes is plenty good enough and over 1 ampere is not needed and NOT recommended.  Connect that charger to the battery in normal fashion, except do NOT plug the charger directly into a wall socket.  Using both a milliammeter and a voltage meter, you will monitor the output of the charger where it connects to the battery.  While you can use just a voltmeter, I suggest both a voltmeter and a current meter be connected. To reduce the charger output enough, fashion a light bulb socket with a incandescent light bulb, connected in series with one of the two power input prongs on the charger.   The idea is that the light bulb you select will REDUCE the charger output.

Of course, you could simply put a 'resistor' in series with the output leads instead of a lamp or resistor in the input circuit.  This is less good of a method since you are not restricting the voltage source in the same manner.  You can even use a huge battery charger (non-smart)...with a resistor or proper lamp.    Depends on how you want to go about all this and what you own.  I suggest you start charging at a voltage only a bit above the existing essentially dead battery terminals voltage measurement, and with a very low current too.   I have tried a number of values of a series output resistor on various walwort chargers, and have found that a 100 ohm resistor works OK on most such chargers on lithium batteries.   Be very careful about the voltage from the charger, and the current flow.  I like to use TWO voltmeters and one current meter, one voltmeter shows charger output, then comes the resistor, then the current meter and then the second voltmeter.  Allow a long time for the charging and rejuvenation.   You do NOT need a large power resistor ...a small 5 or 10 watt one will do fine, even as rejuvenation proceeds and you use smaller ohms value resistors (or, lamps in the AC line or output of power supply line).  

Keep the current down to about 0.1 ampere for the entire early rejuvenation process.  That is not a typographical error, I do mean 1/10th of an ampere.  Charging may take a long time.


I offer a LITHIUM battery rejuvenation service.  I use a highly adjustable digitally controlled voltage regulated source and same for current, and a full set of monitoring equipment.   This service is available only for LiFePO4 batteries.   The cost is about $30, turn-around is a few days.  There is no guarantee it will work on your battery.

Lead-acid batteries:
What are the differences between a flooded battery; sealed & semi-sealed battery; AGM battery; Gel battery; VRLA battery?

1. The two basic types of lead-acid batteries are the type called flooded (or slosh) (a liquid sulfuric acid mixture is visible via vent or cell covers or through an opaque case); and, sealed or semi-sealed type.  Some sealed or semi-sealed types have cell top covers that can be removed in order to add distilled water.  Some types come dry, and you add the acid mixture, but only once, thereafter you may have to watch the liquid level over time. Construction methods can be wildly different.   Batteries of all types need vents, either a tube comes out, perhaps from the side near the top, or from a hole of some sort in the cell caps, or there is a seal (valve) that opens if pressure inside the battery becomes high enough (typically from overcharging or way too rapid charging). Fully sealed batteries can not have water added, sealed means sealed. Some semi-sealed types can have water added if needed. The sealed batteries (and some semi-sealed batteries) differ from the types that have cell cap covers that are easily removed for addition of distilled water.  The difference is primarily in the plate chemistry (typically a calcium component) ...I will get into this a bit next.

2. Almost all fully sealed batteries, that you cannot open, are more properly called VRLA, or Valve Regulated. These batteries have their plates made of a slightly different method and chemistry...similar to a semi-sealed calcium-containing battery.  These sealed batteries contain a one-way valve, and if gas pressure rises too much in the battery, from such as excessive temperature and/or charging, the valve opens, and gases escape. Enough of that and the battery begins to fail as it dries out.  A VRLA battery can have other chemistries such as cadmium, iron, etc. However, all the batteries under discussion here are for those with some form of the element lead, and sulfuric acid as the electrolyte, whether in gelled or paste or liquid form; and, some have the electrolyte solution soaked into absorbent mats.   The valve does not do anything but 'regulate' the over-pressuring possible the use of the word regulating is not all that informative as to its real function.

3. The VRLA group includes GEL and AGM. Thus, strictly speaking, fully sealed car batteries, which always have a gas pressure valve, are also VRLA types.

4. The sealed, and SOME semi-sealed batteries, which I will now call VRLA types, as they all are, use a chemistry called Recombinant. What happens in battery use, particularly charging (something similar, in reverse, can happen under heavy drain) is that oxygen is formed at the positive (+) plate, and the oxygen reduces or eliminates the normally otherwise produced hydrogen at the negative (-) plate. The result is a cycle of gas>>>water>>>gas. This is overly simplified.

5.  AGM, Absorbed Glass Mat, is simply a type of VRLA. You could have APM ...Absorbed Paper Mat, or many other things, but fiberglass mats are very common.

6. Gel batteries have the sulfuric acid mixture combined with an absorbent material, usually powdered silica (sand).

7. A valve vented lithium battery is also a VRLA, strictly speaking.

If you think about the construction, it should be clear to you why the flooded batteries may last longer and more easily take abuse, because the working medium, an liquid acid mixture, is homogeneously in full contact with the metal plate structure, while the absorbed mat can act, under some conditions, like a blanket, the mat itself slows down the transfer of the chemical reaction. It would be very unusual for a flooded battery to have tiny hot spots develop. On the other hand, the AGM battery will have quite low self-discharge.  Another item is that the AGM/VRLA type needs to have lots of plates, because the liquid electrolyte is being presented in a mat, thus, these batteries are tightly packed, leaving less ability for heat-related expansion and contraction.  Very careful design reduces the susceptibility to heat damage.

Voltages for 100% charge vary with the type of battery.  The 'standing awhile' old-style standard flooded (slosh) lead-acid battery was about 12.6 volts at room temperature; the AGM/VRLA/GEL types a bit more, usually 12.7 or 12.8, but some few have up to as much as 12.95; the lithium types about 13.6.  However, just how to deal with these voltages is not clear when you see them in the literature the voltage during actual practical charging, is not that voltage.  I will get into these and other things deeper later in this article, especially about practical voltages.

Rejuvenating tired old lead-acid batteries, chemically:

These chemical additives, such as EDTA, Epsom Salts, etc., are/were often promoted with wild claims.  There is a lot of misunderstanding about the use of these chemicals.   Under the 'right' circumstances, these chemicals, if selected carefully, can or might PARTIALLY rejuvenate old batteries of the flooded type. You need access to the inside of the battery.  If it works, it typically works for a rather short time period.   What happens with lead-acid batteries that are highly sulfated from being discharged or from very old age (just starting your engine causes very slight sulfation every time, & a battery that is partially or more discharged is going to sulfate more rapidly, and perhaps way beyond hopes of recovery), is that EDTA, as an example, can chemically convert the sulfation.  Unfortunately, it can do nothing for the plate the sulfation was on.  The 'converted' product needs a place to go to.  That means it is in contact with the plate; maybe some falls to the bottom of the battery, assuming that the battery even has a no-plates area at the bottom for such deposits.   The active plate may have reasonable 'metal' (using that word generically here, to cover both types of plates in use in batteries) left to do something; or not.  Typically, there is little if any useable active plate material left.  Critically, a sulfate coating caused by a discharge of the battery comes in two types.  What is called 'hard sulfate' from long term sulfate conditions means the battery is nearly totally not recoverable.

My advice:  Don't try using these 'products'.   Even if they work, which is very rarely, the battery is very likely to quickly fail totally, and suddenly  ......and in the meantime it is hard on the rest of the charging system.

Rejuvenating old tired lead-acid batteries, electrically:

If a lead-acid battery has not been moderately to greatly discharged for too long a period of time, you may be able to resuscitate it.   It will not be fully rejuvenated, mostly depending on the time period and depth of the discharge.  You may be able to 'rejuvenate' it good enough to last a considerable period of time.  Flooded batteries that were in reasonably good condition, but have been considerably or fully discharged for not over a month, especially if they were at fairly cold temperatures, probably can be resuscitated.  For AGM/VRLA type batteries, perhaps somewhat longer than a month.   Contrary to popular belief, AGM/VRLA batteries do not like, not at all, being heavily discharged & then sitting that way for any period of time.  In many instances, these abused batteries, rejuvenated some, will draw a lot of charging current (which causes heat, and faster deterioration), and have other characteristics, that cause additional wear on your alternator charging system.

If the battery is quite discharged, terminal voltage may be too low to trigger a Smart Charger to turn-on.  If this happens, you can start the re-charging process by connecting a common low to moderate amperage (a fraction of one ampere to not over 12 amperes rated) common charger, non-smart type, for a long enough period of time until the battery terminal voltage rises above 10 (approximately).  Then disconnect that charger and connect the Smart Charger.  If you only have a simple non-smart charger, watch the terminal voltage. Do not let it get over 15. Watch the current flow too (if you have a meter ...too much current means excessive spot heating).  You may need to connect, disconnect for some hours, then reconnect, repeatedly, until you have 10 volts. If it is a flooded battery, and the water level is now quite low (below the level of the tops of the plates), add distilled water to each cell, as required to barely cover the plates, and charge at a low rate. Do not fill to the normal maximum fill line. Watch the voltage. As the battery charges-up, the acid-laden water level will probably rise some.  After the battery is fully charged, then add distilled water to the normal maximum level line. This can take a week with a very low power Smart Charger (assuming it does turn on), and a day or two with small non-smart chargers. Avoid overcharging, avoid terminal voltage over 14.9.

Before putting the battery into use, & assuming you have been able to charge the battery to at least 14.2 volts, disconnect the charger for a few hours.  Then, use a real battery load tester to analyze the battery's condition.  If you have no access to one, then crank the bike for 10 to 15 measured seconds, without starting the engine.  If the cranking is good, and terminal voltage over 9.5 during the cranking, then you may consider using the battery, as it is probably OK; or, usable to some extent.  No guarantees.

Flooded batteries, additional information

A "flooded" battery usually has removable cell covers, contains liquid you can (or should!) see (wear eye protection) if a cell cover is removed. Sometimes you can see through the case, or use a flashlight or other light through the case, to see the liquid level. You have to add water occasionally to flooded batteries that have removable cell covers.  Water type should be distilled, never tap water. Walmart sells distilled water in 1 gallon plastic jugs for under a dollar, your supermarket price is likely not much higher; ...a gallon will last a long time. Do not use purified water, or de-mineralized water, use only distilled water.

Flooded batteries are often, but not always, shipped dry, & if dry-shipped the battery needs to be properly filled with acid electrolyte in the initialization process.  Sometimes these batteries are advertised as "pre-charged", which is very misleadingThere are several problems involved with the purchase, initialization, and use of a brand-new flooded battery.

There are types of batteries that are not normally considered 'flooded' types, that you do add liquid to ...but just once. Particular versions of Yuasa's Valve Regulated Battery (VRLA) are such types, it is an absorbed mat material type.   After adding the acid mixture liquid, which is more properly called an electrolyte, you seal the battery.  That type of battery is not specifically treated in this article; but is very similar in initialization and charging, etc.  The advantage of this sealed and dry-shipped battery, is that it has a VERY long shelf life, so long as the seals remain UNbroken.   Here is a link to information on that type of battery, and, version not-so-shipped:

If "initialization" of any type of flooded battery is not done correctly, your battery will never reach its full capacity; & will have a shortened life.   It is important that gas bubbles be eliminated now & then during the initialization period & a full & complete soaking of the internal parts accomplished before any high current charging.   This can not be done by filling & then immediately putting it into your bike & then you go for a ride, which also removes a substantial amount of life from your battery.  Filling the battery with acid mixture and initializing the battery is best done by my method, which is better than what the battery maker usually says.

In general, old-fashioned flooded batteries are still the longest lasting batteries, assuming they were properly made & properly initialized and properly taken care of.  These old-fashioned batteries also tend to give you a warning, by slow cranking usually, that they are getting old and tired, which you will appreciate, as opposed to a sudden failure no-warning battery type.

Flooded batteries; or any lead-acid battery under some conditions, can be extremely dangerous.   The hydrogen gas given off by flooded batteries (or, gross overcharging of other types) can cause an explosion from such as a spark from a battery charger connection.  Acid can blind you.  Do not take this warning lightly.  Wear goggles.  Have a container of water available.  Be extra cautious if you remove the cell tops, and try to never have a spark near the battery.  Connecting or disconnecting a charger is a particularly worrisome situation, so connect the charger securely to the battery first (cell covers, if any, not removed!) and then plug the charger into the wall socket.  Do not play with connections at the battery with the cell tops removed and keep metal tools away from the battery.  Even sealed batteries can be dangerous, if grossly overcharged or allowed to get quite hot, as they may pressurize and suddenly open their safety vent (Valve Regulated batteries too).

The conventional flooded battery, with or without 'sealed battery chemistry', must be charged regularly, or kept on a maintenance charger.  Charge more often in hot weather.   These batteries self-discharge more rapidly than other types such as the types containing calcium in the plates ....and AGM and VRLA types have even much less self-discharge.

Some scenarios regarding purchasing and installing batteries:

Scenario #1:
Battery or motorcycle dealer fills the fresh "dry" battery with sulfuric acid electrolyte (one can hope of the correct strength ...German's use a slightly stronger electrolyte), & possibly charges it once, maybe not, probably does not rock the battery to eliminate pockets or bubbles of gas ...and places it on the for-sale-to-you shelf.  Old dealer stock is particularly bad here if the cell tops of the 'shipped dry' battery were not sealed against outside air during 'dry storage', because air always contains moisture, which can begin a slow deterioration of the battery.

The battery begins to deteriorate from the moment of acid mixture installation.  The battery deteriorates especially fast if acid is installed & the battery is not properly "initiated".  The battery sits there deteriorating, awaiting you, the customer.  You arrive need a new battery right now, not later.   If you are lucky, the battery might have been charged & even kept charged.  Improperly initiated? Improperly kept charged? ....your battery may already have lost a lot of capacity, & may already have a decreased life, sometimes a large decrease.  If the battery is older, never had acid in it before, the cell top sealing was removed or never there in the first place, & the battery is stored in an area that has goodly temperature changes during the day/night, & higher humidity ....all these things will conspire to reduce battery life, even once it does have acid mixture put into it.  If not 'initialized' properly, it is worse.

Scenario #2:
The dealer fills the battery while you wait, installs the battery, & you start your engine & off you go down the highway.  Your alternator is valiantly trying to fully charge the battery and the battery is heating up excessively from all the current and spot heating at the plates is damaging the battery. Such a battery has not properly absorbed the acid, will have bubbles as well as small to medium dry places at/in the plates ... creating hot spots & chemical reaction problem areas.  Your new battery will not have 100% of its plate areas initialized chemically nor electrically.  That battery will not last nearly as long as it should, certainly not give proper long life; nor will it operate to its rated capacity & performance.   This type of battery often fails in cold weather rather early; & in some instances can fail in mild weather.  It is possible for such a battery to begin to have accelerated failing in hot weather if you leave the dealership quickly.  You report to a List or Forum that this is a lousy brand of battery.

Scenario #3:
The dealer fills a fresh battery (with no prior air exposure since the cells were still capped & sealed) with acid mixture, initializes it in the way explained later in this article or reasonably similarly, & then connects it permanently to a Smart Charger on his shelf, whilst awaiting your purchase.  The dealer sells these shelf batteries within a few months.   Congratulations!

Scenario #4:
You purchase a battery at Wal-Mart or similar. It is probably a lawn equipment battery. It might even fit with the correct terminal types, size & polarity at the correct places, or you make wood, etc., pads. If the terminals are backwards, you 'make' it work in your bike, putting stress on the battery terminals, etc. ((Hopefully you never forget wire connection direction, as you will fry at least the diode board).   It either is already filled and deteriorating because Wal-Mart does not use chargers ...or, it is empty and YOU fill it with the acid that comes with it ...or you find at some other store.  The instructions that come with the battery are hardly complete regarding initialization.  The battery has no side vent nor hose; fumes are released upwards from cell cap holes.  It is particularly fun when that slow constant release of acid fumes condenses inside the lower seat foam, which also contacts the steel seat bottom.  You find your $$ seat and $$$ seat pan rotted-out and rusted-out a year or three later ...ugggh! You also find the screws for the seat hinges have rusted into their hinge threads, and are the devil to remove.  If you have a K bike, you might find the fumes have caused intermittent problems with 'the computers'.  Do you have other electronics of some sort near that battery?  Did you talk to Wal-Mart before purchase about their specific battery warranty details?  Do you know that if you return a failed battery in, let us say, 3 or 4 months, that the return $ allotment is very skimpy?

Scenario #5:
You failed to notice that the Wal-Mart battery has the + & - terminals reversed. You connect the battery & do a lot of damage to various electrical things in your motorcycle such as ruining the diode board and the $$$ GPS Navigator.  Since the battery does not fit correctly, you return to the store with the battery & find that batteries are covered not by exchange for a correct one (if they have such!), but by an allowance, & you lose a substantial amount of the money you paid for it yesterday.

Another version of Scenario #5:  Perhaps you monkey with the battery leads on your bike 'to make it fit', creating a possible fire hazard ...or, likely, a strain on the terminals ...which eventually produces a sudden death internal disconnect ...and you can then complain about the battery quality, when it was actually your fault. This happens with batteries other than Wal-Mart types too.

Scenario #6:
You return a battery as 'defective', and get you money back 100% ...or, an exchange with the correct terminal placement.  This exchange battery also has no vent tube, and your seat rots out 3 years later, or maybe your bike's fuel injection computer or ABS computer fails.

Scenario #7:
You get the correct flooded battery, with correct terminals in the correct position, correct venting via an overflow & vent tube, initialize it yourself in the correct way, & probably obtain a reasonable life from it, since you also pay attention to maintenance.

Scenario #8:
You purchase a battery.  You use it quite a few years beyond what Snowbum says you should is now 8 or 9 years old (which you are proud of, and let everyone know on the Airlist and Facebook how great your selected battery brand is).  It suddenly goes dead on a dark & stormy night, in the middle of nowhere's ..... & it is Saturday evening ....that means that all bike stores (closest is 125 miles away) are closed for the next two+ days.  It is raining.  You have no rain clothes, no tent, no sleeping bag.  "She" is on her first ride with you.  Things are becoming much less fun at a rapid rate.   You get a passing pickup truck driver to take you, the motorcycle, and the gal, to the nearest motorcycle dealership.  The motorcycle is insufficiently tied-down, and falls over, causing damage to the bike....and disturbing you a lot.   The truck driver takes her to the bus station at her request. You do not get a motel room for two. The pickup truck driver takes you to a motel, where you stay for two days while you await the motorcycle dealership opening; where you find they do not have the correct battery, but will have it for you the next day.  You get to go back to the motel, and pay for another night. The next day, the battery arrives in the afternoon. You install the not properly initialized battery and are on your way, with a considerable amount of battery life already gone.  You have irregular electrical problems on the way home, eventually finding that your alternator brushes are well-worn, and much sooner than normally expected, and your alternator phase leads look overheated .....all due to the original battery being too old. She turns you down for another ride, using a rather lame excuse.

Scenario #9:
You have had many years of use with no problems.  You report that situation on some forum on the Internet, so all the world knows that you have had no problems with your battery brand.   You continue to use that battery with no problems.  Doesn't make much difference what brand nor type it is.   Your alternator & diode board are wearing faster, your starter motor is wearing faster, even the voltage regulator is wearing faster.  The additional wear is due to the old battery ...but it starts your bike problems (so far)!    If you have a K bike or an Airhead with a load shedding relay ....or a particular version of the starting relay,  ....suddenly, one day, that important relay has a problem ...its contacts are welded.  The starter continues to run, as you go down the highway ....and is destroyed ....together with a few other items.  $$$$.

Scenario #10:
You purchase a battery whose terminals are on the correct side of the battery for your bike.  If a fillable type you fill it and initialize it properly.  Your purchased battery was not very old since original shipment to the seller. You charge it on a Smart Charger or trickle charger while monitoring its terminal voltage and if flooded type you do the initialization and bubble removal in my recommended full procedure.  You install it.    You make sure it fits your battery holder/carrier, & that the tool tray does not excessively press down on it when you are seated on the motorcycle. If a flooded type with overflow tube, you install that properly.  You make sure it is kept close to 100% charged. You usually perform a real load check every 6 months, but never beyond one year.  You replace the battery on a time/miles or load testing basis.   Congratulations!

Scenario #11:
You purchase what you think is the best of the best, and pay $$$$ for a Lithium battery supposedly designed for motorcycle use.  It works perfectly,  your motorcycle has never cranked so well during starting.   One day you were tired and hungry when you got home from a ride, and you forgot to turn off the large screen GPS navigator on the motorcycle.  The next day, or the one following the next day, you went to start your bike, and there is a dead battery.    You jumper the bike battery to your car battery, which enables you to start the bike.  You go for a ride.  You are not particularly concerned; and, anyway, your bike has an aftermarket high output alternator, so it can recharge the lithium battery quickly.   The bike starts and runs fine for the next few weeks.    Then, the battery suddenly dies, and can't be recharged.  Unfortunately, the battery death happens while you are on a freeway, in terrible stop and go traffic, it is 110F, and there is 2 miles to PUSH to the next off-ramp, where you remember there is a gas station.  You could call a tow service, but they are not equipped for motorcycles, and would be hours before they can get to you, the cost will be atrocious, and your $6 insurance policy premium for towing is not going to pay.  You are going to be very late for work this morning.  Your pay is going to be docked.  You will need a new battery immediately, $$$$.

Scenario #12:  Your Scenario.

Battery types in common use:

Flooded batteries, by common use of that description (liquid sloshes around in them) are "lead-acid" batteries made in a few basic types.  They contain the element lead, in both a fairly pure form, as well as forms that contain other substances. There are positive & negative lead plates in the battery & they are not the same types of lead substances. The plates are porous. Some types of lead-acid batteries contain some calcium in the plates & those generally have a slower self-discharge, & can be a low or no maintenance type. These best operate at a slightly higher voltage, & thus will work better and last longer if your voltage regulator is set properly a bit higher.  Antimony is another substance often used in these batteries. There are sealed and semi-sealed lead-acid batteries of several types available, besides conventional flooded batteries.  The conventional flooded battery (with or without sealed battery chemistry) must be charged regularly, or kept on a maintenance charger, more often in warm weather.  These batteries do not, generally, require special chargers ...and trickle chargers or standard lead-acid Smart Chargers are very convenient, and the batteries are generally OK with them.

The absorbed mat sealed battery, often called AGM (absorbed glass mat), or VRLA (valve regulated), are, contrary to information published in a few places, typically are the same type of battery.  The AGM is generally just a subset of the VRLA type description. I am not sure where the confusion originally came from, but I suspect it was a German technical school, that taught that the VRLA battery was a flooded battery with absorbent glass mats.  The only battery that might be thought of this way are some from Yuasa (and maybe others?) which are shipped without acid; you fill it; then you seal the battery ...although there is an over-pressure vent.     An example of a battery that is a VRLA/AGM, is the Panasonic brand (at one time, long ago, these were re-labeled as WestCo when sold by WestCo).  The VRLA simply means that the battery has a pressure vent.  Well, so does nearly every 'sealed' battery!

The AGM/VRLA batteries have very low internal electrical self-discharge and are usually shipped from the manufacturer fully charged, and probably will be OK on a dealers shelf for 6 months or so, unless the dealership battery storage area is quite warm.   A popular brand is the Panasonic, a quality battery. Another popular brand is the Enersys-Odyssey, sold as a premium product.  An extra-premium version is available that has a metal case and it may or may not be worth the additional cost to you.  It protects the battery to a great extent at much higher temperatures than the none-metal case common versions; but, it also absorbs heat faster too.  The metal case version is much less likely to have warping effects internally, than the softer plastic case type, and the battery should...or may... last longer (but, can be worse on a motorcycle).  A metal-cased VRLA battery might, in some circumstances, last a very long time ...over 10 years is really possible, even in engine starting usage. I expect that, properly taken care of, an Odyssey in a metal case jacket (they do sell them like that) will last as much as a dozen years in proper use; but I have not yet tested them thoroughly.   I doubt I ever will.

Many 'cheap' and almost always inferior batteries are sold using the Panasonic name in the description. Some are a bit more honest and say they are 'equivalent-to'.  If you want a Panasonic, be sure it comes as branded on the case as the Panasonic.  The Panasonic brand of battery is very well made internally. Yes, I have taken them apart (a quite nasty chore).

AGM/VRLA batteries are usually very tightly packed into their case in order to obtain the extra needed plates.  They tend to be heavier, not lighter, than equivalent AH-rated flooded batteries. The only really important drawback is expansion/contraction with temperature changes (which are from engine heat and environmental conditions and also from high current charging in the bike).  Many early designs failed from 'sudden death' due to internal cell connection cracks, and a few other problems.  With quality modern manufacture, most of these concerns are, or have, faded away, even with the common plastic-cased types.

WestCo stopped selling rebranded Panasonic batteries long ago, as far as I know.  In the long-ago past, one could remove the WestCo label & see the Panasonic label.   After the re-labeling was abandoned, the WestCo battery was probably a relabeled "BB" brand.

Another brand with a decent reputation is MotoBatt. They are hardly the only ones with a good reputation.

Which to purchase:

I recommend you base your decision, on what fits, the CCA and AH ratings, warranty, quality built reputation; and as-delivered cost.  The cost of batteries is constantly changing.  Be sure to think of shipping charges.  You might be able to get a Panasonic VRLA battery from such as DigiKey, shipping free, if you know how to find the free shipping method, usually hidden, on the website (and if that still exists).  DigiKey is a huge & reputable source for electronics parts & other electrical's.   Independent BMW Airheads repair shops may stock proper batteries for you, and usually shipment to you is prompt.

The mats do not have to be glass fiber but most are.  Batteries specifically designed for engine starting were produced originally in only modest quantities; that is no longer so, but back then many versions were not designed for engine starting, and the use of them gave the AGM batteries a bad name, and led to a lot of confusion over the design. The Panasonic was a brand of AGM that was, unfortunately, caught up in this wrong-thinking by many in the motorcycling world, and they vigorously decried the brand, as not being for engine starting, which is absolutely backwards wrong.  There were also truly bad quality AGM batteries sold, and this perpetuated the rumors about AGM.  Now, quality AGM/VRLA batteries are made in huge quantities, most probably as original car batteries ...and as more cars are being produced with start-stop-start-stop type of engines, most all will have AGM batteries of some sort.

Before these batteries were finalized in design for general public use for vehicle starting, they were developed for the Military and for extremely long life.  Float/maintenance charging was used with very specific voltages to be supplied to them.  These batteries were slightly later used for electronics and other back-up systems, often systems that are hardly, if ever, looked at.   Somewhat modified versions of these batteries were later made for engine starting and became very popular. Absorbed Mat batteries designed for vehicle starting & charging systems are used in automobiles where demands on the vehicle battery are typically higher than with flooded batteries.  Quality AGM/VRLA batteries are generally quite sturdy & very tightly compact internally. The batteries in the same AH capacity are usually heavier than flooded batteries. High heat and/or vehicle starting and/or high charging currents are all somewhat damaging to them, so once in awhile a catastrophic failure still happens, suddenly the battery is essentially dead for starting, although the lights may work, due to an interconnection corrosion/cracking failure. Generally, the car versions are in stiff cases, the motorcycle types not so much, so they have a somewhat more tendency to swell upon overcharging and high temperatures.  The reliability of the best AGM/VRLA brands is quite good.

MOTOR Magazine (a top source for Professionals, for everything about repairs & also industry trends) expected that by the end of 2016 about 40% of all new cars and trucks would have AGM batteries, & the rate of installations would increase.  One of the reasons is the ruggedness.  A major reason is the new idle-stop technology being rapidly introduced to improve fuel economy & reduce emissions.  In that mode of service, engines might be automatically stopped and restarted up to 50 times a day in normal city driving.  AGM batteries designed for stop-start use will handle three to four times the number of reasonable depth of discharge/charge cycles compared to conventional batteries; they will accept higher charge rates; operate better with lower charges, provide higher cranking performance, etc.   For motorcycle use, the designs have greatly improved and now they are not known for their previous catastrophic failure modes. For automobile use, the alternator systems are big, rugged, and the future (already beginning) will have the alternator and starter motor combined into one unit.

All the various types of lead-acid batteries, whether sealed, gel, lead-calcium, lead-antimony, VRLA, AGM, etc., have somewhat differing charge & discharge characteristics. Other things also have varying effects, such as self-discharge, temperature, etc.  Some variances in charging voltages, particularly for various levels of the highest level of being fully charged, are also applicable. This article will get into these things, in some depth.

True gel vehicle batteries, such as the $$ BMW (Exide) types, do not use the same absorbed glass mat construction of the VRLA Panasonic, AGM, etc.  Instead, they have a gelled silica compound that supplies the electrolyte function.  The form of gel batteries used for low-drain home-security systems, and even in some power backup systems for computers, is not the same as the BMW gel battery.  The BMW Gel battery is being used in a standard charging system bike and the stock VR does not perfectly match the gel battery's needs.  If you use a maintenance Smart Charger on a BMW or other gel vehicle battery, the specifications need to be relatively tightly controlled, & the voltage level need is slightly higher than the stock VR delivers.  It is a compromise, in my opinion, for BMW to offer a gel battery like this, for a bike with a standard charging system, often charging at too low a voltage, as set by BMW originally.  Luckily, the voltage regulator in the Airheads is either adjustable or low cost adjustable ones are available. For the Classic K bike the VR is part of the brushes assembly inside the alternator, & can be changed to the higher voltage version with some effort, as you must remove the alternator and disassemble it. If you do not change the voltage, and the voltage at the battery terminals, during cruising, is in the stock area, say between 13.7 and 14.0, you will still get 'reasonable' life, just not quite as much life as if the charging voltage was 14.3 or 14.4.  In my opinion, vehicle GEL batteries are not as good as other lead-acid batteries, when the temperatures are near or at or below "freezing" ...that means water freezing temperature:  32F.    FYI:  "Authorities" VR's are usually set to about 14.4.

Many of the aftermarket batteries, such as the AGM/VRLA types, are slightly taller, & often much less wide, than the stock motorcycle battery.   Some Panasonic and many other batteries that are slightly taller than a stock/standard BMW Mareg flooded battery, will be pressured by the Airhead tool tray ...not a good idea because when you are sitting on the seat you can possibly damage the battery over the long term.  There are several fixes I have used for this.  How to deal with this varies due to motorcycle variances.  The distance from the bottom of the battery box to the underside of the tool tray is not always the same. There are differences in the seat pans, rubber bumpers on them, & possibly some small but accumulative tolerances on other things, such as at the battery lower mounting, etc.  I advise you to consider the actual height of the battery you will be purchasing ...and your tool tray fitment.  I will assume here that you have accepted that there will possibly be minor things to take care of, have purchased such a battery (perhaps the excellent Panasonic). ...and, below are ideas on how to deal with the battery (if need-be).  Motorcycles vary and installations will vary, so try what works for your bike.  Always think "safety".  You do not want a metal hold-down to electrically short the  terminals, so I made my hold-down straps to go across the approximate middle, so this was never a problem. I have also used combinations of these things, especially using both #2 and #3.  I have sometimes made a wood spacer for the narrower battery & painted it black; but later found out that normal hold-down pressure was plenty enough to keep the battery from moving, even in rough terrain.

1.  Make a flat hold-down plate, perhaps from a piece of some sort of steel or aluminum.
2.  Sand down the unthreaded part of the plastic hold-down knobs threaded hole area. That shortens them a bit.
3.  Turn the stock metal-type battery hold-down upside down. That also lowers the top of the knobs.
4.  If the knobs are not sanded, & just put in upside down, that sometimes works, but if you also put the stock hold-down upside down, that may make it less easy for your fingers to rotate the plastic knobs.
5.  Your method.

De-sulfating types of chargers:

There are smart chargers that have a de-sulfating mode.    These chargers are generally OK for use if the battery has ...perhaps ...a quarter charge ...or more.  De-sulfation chargers do work 'sort-of', at least sometimes, but if the battery charge was quite low for any goodly period of time, de-sulfation modes, if they work at all, will be unlikely to give much more battery life, compared to you using a standard charger, or a smart charger without de-sulfation protocols, in trying to resurrect the battery.

WARNING!  If you use a de-sulfating mode on a battery that is fully connected to your bike's wiring system, the high voltage much as 25 volts! ...and in some instances,  a large steep voltage 'spike' that is very short in time from the charger ....can injure the bike systems! ....and can injure some types of electronics you may have on the motorcycle.    The risk of expensive damage is particularly so on CAN-BUS bikes.  I highly recommend that you be very prudent & never use de-sulfation mode on a Can-Bus bike! ...and think before using that mode at all on any motorcycle (or car).  If you do use such a mode on such a motorcycle, there IS a safe way to do it! Disconnecting the battery from the motorcycle is the safe way.  If you remove the battery from the bike, or at least disconnect it (disconnecting all wires to the negative terminal will do), then there is no problem with using a de-sulfating mode charger on any bike.  Do not use such a charge mode with lithium batteries! ...not ever!!

Whenever any type of lead-acid battery is at less than full-charge, there are chemical reactions going on that are causing faster deterioration than if the battery was sitting there, fully charged.  Said differently, much lower deterioration or aging is still happening at full charge. There are several types of deterioration.  The one most commonly talked-about is sulfation.  Sulfation, put overly simply, is the accumulation or plating of an electrically insulating chemical onto the otherwise active plates in the battery.  The sulfation process is a chemical change using the 'sulfur' molecule from the sulfuric acid mixture, and this effect occurs much faster as battery charge decreases.   Initially, the deposited sulfate crystals are what are referred-to as 'soft'.  These 'soft' crystals can usually be chemically converted, or mostly, by such as charging properly, which can very substantially remove/convert these sulfate crystals, which are otherwise being accumulated (plated) onto the battery plates.  Recharging the battery can usually recover almost all the original capacity & proper function of the battery.    As the battery charge reduces, over time, from the battery not being recharged, the sulfation gets worse.  Enough time at a reduced charge, particularly a deeply reduced charge, & the small sulfate crystals get much larger & these are often called HARD crystals, and ARE vastly more difficult to remove or convert.    Eventually the battery is ruined.

Various chargers on the market may promote their anti-sulfation or pulse modes, or other wordings.  Some do work fairly well; but, many, if not most, are only partially good at reducing sulfation; and hardly do much for the large hard crystal type of sulfation.  A lot of the advertising is false or very incomplete.  If you want to desulfate a battery yourself, you can attach a quite small (very low output) battery charger & monitor the current & the voltage.  Because chargers vary so much in true output voltage & current (also depending on the battery!), it is impossible to give hard & fast rules here.   Those with the know-how & the equipment can use an adjustable power supply, or a charger with a series resistance, or a quite small charger (1 ampere, perhaps, but some up to 3), or a larger charger with a method of reducing the charging current/voltage (a series connected lamp bulb perhaps, or Variac on the line side of the power source).   Whatever the method, the ideal way of trying to relatively quickly remove/convert early sulfation to nearly the extent possible, is to charge the battery at about 0.150 ampere for a day or even three days.  Since there is no quite high charging pulse voltages in use, and only a quite low current, it is safe to do this with the battery still in the bike, and even if still connected.  Don't go over 16 volts at the battery.  You could do it faster by starting off with no more than 1 ampere, never exceed that amount, & keep raising the voltage as the charging current tapers off from the battery obtaining a charge.  The lower value stated above, 0.150 ampere, is best.  An even faster method than the no more than 1 ampere method, not quite as good, but still likely good enough, is to charge at a much higher rate, perhaps up to 6 amperes for a few minutes, then 3 amperes for a some time, all watching the terminal voltage.  When the voltage reaches about 14 to 14.5, reduce the charging current to 100 to 150 ma (0.1 to 0.15 ampere), for several days ...checking the current now and then, and adjusting the source if needed to maintain the proper current.

There are other types of deteriorating conditions, including one called stratification, where the acid & water mixture separate some, & the acid is near the bottom.  This situation is also helped by the very slow charging methods in the prior paragraph.

Very long term charging can be done at 0.04 to 0.06 ampere. This is the type that might be considered for a very long storage period, and/or de-sulfating.  A simple tiny low-output charger, with a series resistor, will do this. This "extremely long term trickle charging" is, as noted, done at 0.04 to 0.06 ampere.  You do not need a $$ smart charger to set up such a low charging amount ...if you don't know how, ask on the Airheads list or Kbmw list, etc.  In fact, many Smart Chargers will not even go this low.  This method can sometimes be used with a Smart Charger after a complete and full charge. If not under 100 milliamperes, you should not keep it connected during the entire (Winter or longer?) storage time ...although the deterioration will not usually be excessive.  Some Smart Chargers have periodic cycling, so it can be more hassle to measure and determine the present mode in use. Thus, the very cheapest teeny chargers, with a series resistor (or appropriate lamp can be used for that purpose) are really best for extreme long term storage. Many just use a Smart Charger ...which will not deliver the longest life for your battery as will the 0.04 to 0.06 ampere setup.

I know of no Smart Charger manufacturer that will tell you these things!

Things to know:

The higher the temperature of any battery, the faster the self-discharge, and the more need for re-charging.   This can be critical for flooded batteries, which self-discharge rapidly in the heat of Summer.   VRLA, AGM, Absorbed Matt, and Gel batteries have much lower self-discharge, although their self-discharge rate does increase as the batteries age.

Some manufacturer's do not furnish important specifications when promoting & selling their products.   Some, on purpose, try to cleverly avoid information such as Cold Cranking Amperes (CCA) by using other terms that are of no importance, or even meaningless.  CCA is how many continuous amperes the battery will supply for 30 seconds at 0F ...before the battery voltage falls to 7.2; where its energy level is essentially zero.  Your motorcycle would be unlikely to start at such a low voltage, but the specification is a strict industry standard, so it is very useful for us.   Said another way, true CCA, as far as real world use, will be somewhat less than the CCA as advertised, because the battery is not usable for starting the engine at 7.2 volts fact, under 10 volts is getting very iffy.  Nitpicking aside ...the CCA test is real world useful.

CCA, combined with what is called Reserve Capacity, is what is important, besides quality and fit. Reserve Capacity is specified for 10.5 volts, so it is real-world usable ...IF you can find that specification (and, find CCA).  CCA is obviously important in cold weather.

A brand-new battery will start deteriorating immediately after being put into service, which is one reason batteries should be tested yearly, at least, by a load tester instrument.  I will have more to say on proper use of such a tester.

"CA", a calculated value (as opposed to CCA), is done for 32F, and is pretty-much worthless.   Nerdy: On good quality batteries, CA is typically going to be CCA divided by 1.25.

I think a reasonable practical test, which is pretty much a common Load Test, is, at "room temperature", 10 to 15 seconds at 3 times the rated ampere-hours (or, better, more stringently, at 1/2 of CCA rating), at which the battery, while under the testing load, should read over 10 volts.  This means that if you load test a 30AH battery by having a load of 90 amperes, and maintain the load for 10 to 15 seconds, that battery should be considered good if the voltage is over 10 volts at the end of the load testing time (load still connected at that point). A good Load Tester has compensating charts or readout correction, for temperature.  The inexpensive two-meters load tester from Harbor Freight is quite adequate, and useful for motorcycle and cars and trucks measurements, and easy to use.  It is better than the one meter unit they sell, although that one is cheaper, and adequate-enough, for motorcycle batteries.  NOTE that using 1/2 the CCA rating is a better test. For whatever test you DO, watch the voltmeter which is part of the tester, or, have your own digital meter connected to the battery posts ...the voltage must NOT sag quickly.  A few tenths drop over 15 seconds means the battery is VERY likely to be in VERY good condition.  A faster voltage drop means the battery has aged considerably, and while it is a judgment call from experience, I replace a battery that, immediately after I spin the knob to raise the current to 1/2 CCA value, shows a sag of more than 0.4 volt, for the nominal 15 second testing time at that 1/2 CCA loading.   Few seem to know of doing this specific voltage sliding effect, but it's a really good one!   A NEW battery won't hardly move its voltmeter needle at all.

Batteries deteriorate, fully charged or not.   Deterioration varies with temperature & type of battery.  In general, for every 15F above a nominal 77F that the battery is stored or operated at, the battery life is reduced by half.

Batteries self-discharge.   A flooded battery loses about 1/4% to 1% of its charge every day in very hot summer temperatures.  For an AGM, the loss is much lower, perhaps 1-3% per month. These figures are for batteries being stored with no loads attached (not even electro-mechanical clocks) and the motorcycle is not being driven during this storage time.

When you charge any type of battery, the conversion is not 100% efficient.   For flooded batteries, you must put into the battery about 15-20% more electrical energy than the battery will give back.   This 15-20% is converted to heat in the battery during charging.    For AGM's, the conversion is more efficient, perhaps as low as a 5% loss in efficiency (The lithium batteries may be even better).   Yes, it is true, this does mean a AGM-VRLA battery can be 'easier' on the charging system than a flooded type.

Nerdy (more!):

There is a peculiarity with all types of batteries (but, the level of that peculiarity varies with the type of battery) ...that deals with a mathematical function called "Peukerts Exponent".   What it means on a practical simplified basis is that some batteries can be discharged (there is a re-charge effect too) at a higher % of capacity rate than others, with a minimal or less loss of total capacity.  That does not seem to mean much; or, requires you to sit here, and re-read it 10 times ...and still not understand it., a reverse way of thinking about this is going to be explained here:

Let us suppose you have a fully charged battery of any type & in good condition.  Let's say that battery has an ampere-hour rating of 28 AH.   A 28 AH battery should, by simple mathematics (only), deliver 280 amperes for 6 minutes; or, 28 amperes for 1 hour; or, 2.8 amperes for 10 hours; or, 0.28 amperes for 100 hours.

Batteries are devices that use chemical change to produce electricity, and the process is less efficient as current drain goes up.  Thus, a battery typically loses true output capacity as the drain rate increases.  YES...this means that as the drain rate increases (you use more amperes for any given period of time), the REAL Ampere-Hour capacity goes down.  Your 28AH battery is not a 28AH battery when the drain is 'high'.  Just what is 'high' depends somewhat on the manufacturer and type; but, as a general rule, anything over 10% of the AH rating as a drain, starts to reduce the practical amount of AH available, more or less depending on the battery type and quality of design/manufacture.   The AGM and GEL batteries and, in particular the lithium batteries, are less affected than the flooded types.   Another way of thinking about Peukerts, is that a huge electrical load on a lithium battery, and to some extent a AGM battery ...will not effectively reduce the total ampere-hours capacity nearly as much as it would on a flooded battery, because the Peukerts value is less for the Lithium/AGM/GEL/VRLA, compared to the flooded type.

There is another peculiarity, not directly a Peukerts thing ...AGM/VRLA batteries can deliver somewhat higher voltage at the same time as having large loads.  Yet another way of looking at all this that the rated AH is more usable in high loading conditions on those batteries ...such as repetitive cold weather use of the starter motor on hard-to-start bikes, over and over, within a minute or three, perhaps.  These batteries also have another peculiarity...on a cold day, a heavy loading will heat the battery plates more than a flooded battery, and so give a bit better performance after a few starting attempts, due to the increased chemical activity in the mats and plates.  It is a small, but measurable, effect.

The terminal voltage drop (reduction) on many of these newer type of batteries is flatter ...the voltage drops a bit very quickly; then remains on a rather slow downward curve, until it suddenly falls off steeply.  This is, for most folks, very good ...but you get less warning notice about the battery going dead. Lithium batteries have a particularly steep function; and go dead very fast when the charge is depleted beyond a certain point, and the load continues.   We call such fast voltage drop-offs in a battery as the battery having 'a very steep discharge curve'.

HINT:  When a battery is old or getting closer to failure (even not very old batteries can start dying), if your stock BMW dash voltmeter is wildly swinging during use of the directional (trafficators) flasher, & you have already checked the wiring and connections at various places, the battery may need replacing.  There can be other causes for the voltmeter swinging, especially poor switches and connections.  Check the battery using a Load Tester and note the voltage change during the testing.

Proper way to fill & initialize a 'dry-shipped' flooded lead-acid battery:

This type of battery has visible liquid in it after you fill it.  While you should look at the manufacturer's information, the information in this section is better than what most manufacturer's have in their printed instructions.

The battery must be filled properly and must sit at least overnight before being used in your motorcycle, and you should charge it overnight, but only carefully ...which is all explained here. Proper Initialization, which may here be somewhat more complex than the battery maker says, will lengthen battery life, with a small amount of extra effort.  Here is how to do it properly:

1.  Put the battery on your workbench, floor, wherever (concrete floor problems are old wive's tales stemming from leaky wooden battery case days).   Put safety goggles on.  Fill the cells to the upper fluid level mark on the battery using the acid mixture provided.  Install the cell cover(s).   Let the battery stand 4 to 8 hours settle in and cool down ...because the acid installation causes some heat (worse in hot weather).  Some battery manufacturer's will say 1 hour minimum.  An hour is not enough time, to fully saturate every internal area.    During my 4 to 8 hour period, occasionally shake/rock the battery to get bubbles released.  I do this by rocking the battery back & forth, giving it a bit of a 'knock' on the table/etc., as the bottom angularly bangs the table moderately.  You want to dislodge bubbles that are formed so as to ensure all parts of the battery are fully wetted.

2.  At the end of the above period top off the battery cells again, to the same upper fluid level mark, using the same acid mixture.   Note that this is likely the last time you will ever add acid mixture to the battery ...but, don't throw the acid out as sometimes a battery may require topping up after being fully charged & after it then sits overnight.  I keep left-over excess acid here for etching & other purposes, such as rust/scale removal from steel, etc.

3.  After above step 2, and when the battery is at or below baby bottle (luke-warm) temperature, then you may start charging it.   Connect the charger's battery leads carefully & securely, & then, not firstly!, plug in the charger; this is to avoid sparks.   This is especially critical during anytime the time the cell caps are off, so be sure the cell covers were replaced before using any charger.  Wear goggles.    Never connect or disconnect a battery charger unless its power plug is unplugged from the wall socket first ...that  avoids sparks.  Have the cell caps in place when playing with the charger or other wiring!  Please pay attention to my advice here, which is all for your safety!

4.  The rate for initial charging of a new flooded battery is officially a maximum of 10% of the battery ampere-hour capacity.  If you have a 28 ampere-hour battery, that means 2.8 maximum amperes.   I do not recommend small chargers rated below 1-1/2 amperes for initialization, although if that is all you have, then use it.   On a practical basis, you will likely be able to use even a rated 6 to 12 ampere car-type charger, as long as its meter indicated charge does not exceed 20% of ampere-hours rating for more than a few minutes ....before the charge rate tapers down.

5.  Discontinue charging if the battery warms up much over luke-warm, and then restart charging after the battery cools down.

6.  Some of the small ''wall-wort'' chargers (small black box chargers that plug directly into the wall receptacle without any power cord to the wall socket) will have internal circuit breakers that will constantly cycle on and off during initialization of some types of new batteries; and that can possibly burn out these low output wall units.

7.  When a dry battery has acid mixture first put into it, the battery will automatically gain a certain 'charge'.  This is the  'dry-charged battery' effect.   For most batteries, that charge is close to 80%, if the battery was properly filled & let stand for some hours.  If you put the battery into immediate use on a motorcycle, without waiting, a number of bad things can happen, including spot area overheating which can loosen the lead compound mixture which is pressed into the plates grids. Even with waiting some hours, the motorcycle alternator may charge the battery at a vastly too high rate; or, the battery may be discharging if you have a bike with many lights or poor alternator output, etc.   I strongly advise you not put a new battery of any kind into service until you properly charge it fully.  For a typical lead-acid battery, this means that terminal voltage after charging & after letting it sit for at least hour with charger turned off or disconnected, will be 12.6 to 12.7 volts.  If the battery is still being charged, and at a low rate (10% of AH or less) for a long period of time, and the voltage has risen to 14 (up to 14.9 on some types)...then the battery is fully charged.   A more accurate indication is the battery voltage 1 or 2 hours after being disconnected from the charger is  ~12.6 to ~12.7.

8.  The amount of time necessary to charge a battery, considering chemical inefficiencies, can be as long as, but not necessarily is, in hours, the rating of the battery divided by the average charging rate, plus as much as 50%.   I have seen it even longer with constantly cycling wall-wart chargers.   Batteries vary with voltage rise during charging.  Be patient!  The last part of the charging process may take considerably longer than you may think it should.  Some batteries will have a rather suddenly quicker raise in the terminal voltage as the battery is very close to a full charge, so do not abandon checking the battery for too long a period of time.  This type of fast voltage rise is particularly common with such as the Odyssey battery, and it could rise over 14.9, which is not a good thing to have happen.

9.  The better Smart Chargers (lots of brands) are very nice, and most can be left turned on for extremely long periods (years in some situations). However, such extremely long-term constant usage is always detrimental to battery life, unless the current flow is very low ...really low! ...not much over the self-discharge rate; and all of the Smart Chargers I have tested have too high an output for such super-long term 'on'.  I have written about such very long term storage trickle charging earlier in this article, and how to do it safely.   You will find flooded batteries under such constant Smart Charger use to dry-up, that is, need distilled water to be added, and often this is within perhaps 4 months, most require it long before a year is up.

10.  A majority of all the smart chargers I have seen have insufficient temperature compensation. Because of this, many do not initialize a battery well, nor maintain it well, particularly in cold weather.  These smart chargers seem to be set for a compromise voltage. I prefer initialization of a new battery using a common type of non-smart charger, if you monitor the temperature and voltage of the battery.

11.  I suggest you monitor the new battery for temperature of the case (by feel is OK), just to be sure it is not overheating, & monitor the battery terminal voltage with an accurate digital meter now and then.  The battery terminal voltage will slowly rise as the battery charges.  This rise can be quite non-linear.  That is, it is possible for a rapid small increase, and then hardly any increase for long periods of time, until the battery finally reaches full charge and perhaps then the voltage very quickly spikes upwards.   The speed of voltage rise, and the voltage reached after many hours, is dependent on the internal characteristics of your charger, and the type of battery.  It takes a minimum of 12.8 volts at the battery, for a very long time, to come close to fully charging a battery; but this is not the same as initialization!   12.8 volts is not nearly high enough to ensure a properly initialized battery.  The voltage should be considerably higher, typically between 14.2 and 14.5, but not over 14.9.   These are at common 'room temperature'.

12.  For both the flooded and VRLA/Absorbed Mat, etc., batteries, the maximum initializing is 13.8 volts, per many books. That is not correct.   In truth, up to 14.9 volts can be used, and I suggest 14.2 or a bit more for flooded batteries and 14.7 for the AGM batteries.   It is better if the charging current is kept modest.

13.  Some literature will say there is an official sweet spot at 13.2-13.5 for flooded batteries.  You might well disregard that, I find it rather wrong for initial charging, and the whole idea of a 'sweet spot' is never explained.   The only thing you might want to know is that the voltage is the reasonable voltage for rather warm climates for the maintenance mode on a smart charger.  This has confused many a person.  I suggest you disregard all of this for initialization of a new battery!

14.  Battery voltages for charging are typically quoted based on 25C temperatures (77F).     Battery charging is ...or can be ...controversial, ....with manufacturer's selling their own chargers that are touted as very special (only some few are).   For flooded batteries, no matter the calcium or tin or antimony or selenium added to the chemistry of the plates (or not), when re-charging, it is a good idea to charge to at least 14.2 volts, and 14.5 is good.  I'd not go very much higher; and I'd keep the battery at those voltages for quite awhile, for a full stabilization charge.  Afterwards float-maintenance charge can be in the 13.8 v. area.  Flooded batteries are quite tolerant.

For AGM/VRLA/ABS such as Panasonic, WestCo, most of the 'Chinese' AGM batteries, and the Odyssey, ETC. ...I recommend (for the very longest life) that the charger be capable of almost half the A-H capacity of the battery.  Most won't have that powerful a charger, but you will only loose a truly small amount of life if you do not.   For bike batteries in the 14 to 32 AH range, you really need a charger rated at 3 amperes or more; and ones under 2 amperes are not good for longest possible life from a battery.  This idea of a minimum charger capability only applies if the battery was heavily discharged when you started to recharge it.   This is a real peculiarity, but it is true.   If a battery is being initialized from brand-new, a 6 ampere to 12 ampere charger usually works quite well for a bike battery.  This usually is also applicable if the battery is deeply discharged. Keep in mind what I previously said about the tapering of the charge rate within minutes.

If the battery has been in use for some time, and the discharge amount is not great, you can certainly use a lower output charger.  If the battery is not new nor deeply discharged, any common low power charger will suffice, even if well under 1 A rated.  Yes, again, a peculiarity of lead-acid batteries of all types.  I'd not go overboard on using this information though.

15.  A bit nerdy:  Once a battery is charged to ~14.0-14.5, it is close to fully charged,  but not quite fully charged. There are various effects including "surface charge" going on in the battery.  In order to complete the charging, it is best to continue charging at a lower voltage, for a number of hours, perhaps overnight. That voltage is about 13.6.   Because of this, Smart Chargers get a bit extra life out of batteries just from that particular characteristic. Further, any charger must be capable of producing at least, during the initial charging ...a minimum ...of 14.2 volts, especially on the Odyssey.  Odyssey's have a peculiarity ...or, well, somewhat.  This information applies pretty well to all lead-acid batteries.  Let us say you have a quite well-maintained and not all that old Odyssey battery.  You use a small wal-wart charger, not a smart charger, every month or two, the battery is mounted in your bike, you have a clock that draws a teeny bit of power, maybe something else (or not).  The battery voltage may read quite well before charging, but you know that best practices are to charge to about 14.5 to 14.9, now and then.  When you start charging, the battery might be 12.3 to 12.55.  That voltage will rise very slowly, and then much faster rising will occur.  That's normal! Be sure to disconnect the charger, or unplug it, at 14.9 maximum on your digital meter; I use 14.8 to 14.85 as an absolute maximum!

My suggestion is to charge relatively quickly to 14.7 volts, and then, if using a smart charger, float/maintain at ~13.6 volts.  No matter the type of charger, smart or not, you certainly can disconnect the charger if you want to, after the charge is at 14.7 and the current is maybe 100 ma.

Even more nerdy; you can calculate the change in value, for other temperatures.  If the battery temperature is colder, the voltage need increases.  The calculation is 24 millivolts per degree Centigrade, referenced to 25C.  Thus, if the battery is 10 degrees warmer than 25C, the optimum voltage is decreased 240 mv.   I leave you to change to Fahrenheit, and calculate your conditions-effects. Later in this article will be more about voltage/charging.

16.  Going back to brand-new flooded type batteries being initialized:
You have already filled the battery, done the rocking and tapping, refilled as required, and the battery has sat for some time, etc.

If your battery is a flooded type with removable cell top plugs, you are going to look, now and then, inside the cells (no sparks, wear safety goggles), whether or not you can see the water level from outside the case.  I recommend that if you look at the water level with cell caps removed, that you unplug the charger from the wall outlet first, as a safety measure to avoid sparks.    After some hours (usually), the new flooded battery charging voltage will begin to rise close to 14 volts & the cells will have many small bubbles starting to rise; depending on the charging current.  The higher the charging current rate, the more bubbles.  You may not see bubbles if the charging current is quite low; and, it may not happen anyway for quite some time.   Assuming a decent charge rate (current), and after an hour or two of bubbles rising, all the cells should be 'gassing-bubbling' at about the same rate.  The amount of gassing is absolutely current dependent, once the voltage is high enough.  More current, more gassing bubbles.   It may well be difficult to see any gassing-bubbles if your charging current is low, perhaps 0.25 to 1.0 ampere.  You do not have to see gassing bubbles.  Your eyeball, with goggles on for safety! ...will easily notice if the bubbling is happening, & that it is about the same in all cells if the current is high enough (say 10% of AH capacity, which means 2.8 Amperes for a 28 AH battery).  Be patient.  Do not move the wires, ...avoid causing sparks!

When all cells are gassing (flooded type battery, with enough current flowing ), and/or the voltage is perhaps 14.4 at room temperature (closer to 14.9 at 50F or colder) then the battery is usually considered fully charged.   You can remove the charger, and let the battery sit an hour or two, then recheck the terminal voltage (accurately, please!),  ~12.6-12.7 volts is to be expected.

For some batteries the gassing point might be reached a bit lower, or a bit higher.  Do not let any battery type get over 15.0 volts at room temperature.  Try to not let the battery get much over baby bottle temperature.   If the current is low, and you can't see gassing, use the voltage measurement, and allow extra time.   Conversely, if the bubbling is quite evident, and you are only at 14.4 volts, and the bubbling is the same in all cells, the battery is likely fully-enough charged if the current is low, perhaps less than one-half ampere to as much as two amperes, depending on your charger.  Smart chargers are not in this category!

17.  With sealed batteries you won't be looking for bubbles, but you will be monitoring the terminal voltage.  The exact point at which you stop the charging is not critical.  I recommend between 14 & 14.9 volts, this varies with battery construction, materials, and temperature.   Some Smart Chargers may not allow that much; or produce it then quickly go lower, and you might not see that happening, which is why I like non-smart chargers for initializing and first charging.

18.  Unplug the charger from the wall and then disconnect the charger from the battery.  This avoids sparks.    Sparks are very dangerous around flooded batteries ...and can be even on some sealed batteries.

19.  For a flooded type battery, or a 'fill-it' type of AGM, etc., you can now install the battery into the motorcycle.  Mechanically (sandpaper?) clean the wires before attaching them tightly to the battery.  Be sure the battery terminals are clean and shiny. Be sure the wires are oriented to avoid shorts & sparks and avoiding strain on them and the terminals.  It is a good idea to purchase some of the goop in a tube (NCP2 or equivalent or at least Petroleum Jelly, often called Vaseline, in the USA).   Coat the entire positive (+) terminal, and + wires metal ends, after assembly; ...and, if the insulation is poor, force some into the wire/insulation junction.  Use an old hardware store 'acid brush' or old toothbrush suitably modified for this coating.  It is not necessary to goop the negative terminal area.  It is also OK to use clear silicone grease for this.  The best product might be the special anti-corrosion grease stuff for batteries, it does not depend on just the grease barrier, but incorporates anti-corrosives.  The gooping is to prevent atmospheric effects onto the terminal connection.

20.  Monitor the battery voltage at the battery & start the bike.  As soon as the cylinders have some modest warmth, increase rpm, watching the voltage.  Allow a minute or two, depending on how much you used the starter motor.  If it does not reach 13.7 minimum; 14.5 maximum (although 14.9 is OK at quite cold temperatures) as the rpm gets higher & higher (might take 4000 rpm depending on the lights, etc. you have), then you have a problem with the charging system or excessive loads of your bike, which needs looking in to.   The voltage regulator should not be hot from a previously run engine for this test, unless you use a lower voltage for that temperature.  A high VR temperature should show lower charging voltage ...up to a few tenths of a volt. The VR in K bikes is internal to the alternator, so you can't check its temperature by feel ...but the alternator case is good enough. 13.7 volts is low, and battery life will likely suffer.  For a good relative value, at 'room temperature on the voltage regulator', the engine not yet having heated up the regulator, or regulator inside the K-bike alternator not yet heated up, .....use 14.25 volts.  This is a truly good compromise between battery life, lamps life, etc., although as much as 14.4 can also be used.  If the charging system is in good condition, and that includes all connections, even in the ignition switch!, and the voltage is too low, perhaps you should adjust the VR or get an adjustable one.

21.  It is typical for a stock BMW Airhead fairing voltmeter, to read 0.2 to 0.5 v. lower than an accurate digital meter at the battery itself would read.  If over .35 volt difference (headlight on) you may want to check the fairing voltmeter calibration, & if OK, then check for resistance at various contacts, relays, & connections, beginning with the ignition switch. Be sure to check the small starter relay pass-through internal connections under the fuel tank, as all current flow to the system except the actual main starter motor power, flows through that relay's internal connections ...and, its socket connections; BMW uses red wires on those connections.  Check for voltage drop between red wires. You may need to fix that wiring, or open up the relay and fix a loose rivet on the jumper, or, whatever.   Poor connections at the battery wires (either ends of them) will almost surely lead to poor performance.

22.  On BMW Airheads, poor grounding connection at the diode board or not tight enough connections at the board or the alternator can cause charging problems ...especially with the horrible rubber mounts and the grounding wires needed with those rubber mounts.  I strongly suggest changing the mounts to aftermarket metal ones.  There are certain models that can have timing chest to engine problems with painted touching surfaces, etc.   Lots more in this website.  Fix the situation here before doing anything more.   NOTE that on Airheads, black factory paint on the timing chest surfaces where the timing chest meets the engine are ALSO the cause of minor voltage regulation errors.

23.  If you store your bike for the winter, removing the battery is usually not necessary, so long as you keep it reasonably charged.  A fully charged battery will not freeze in typical, even quite cold temperatures, takes 50 below zero F or more on a fully charged battery.  If the bike is stored, and won't be recharged or used with a smart charger, you probably should remove it from the bike.  The colder the battery, the less often it requires recharging, and using small trickle charger is fine every month or so.  A Smart Charger can be connected & plugged in all the time, according to many Smart Charger manufacturer's, but this is not the very best for the battery, contrary to common belief.  Best to use the Smart Charger every month or even three, for overnight. You can leave a Smart Charger on all the time, but expect a small to modest decrease in battery life; something the charger makers never tell you.  If you have a flooded battery, do check the water level every two months, no matter what type of charger.  The water level is best checked with the battery fully charged.

Very long term non-smart-charger trickle charging can be done, at 0.04 to 0.06 ampere. You will need to use a small lamp or resistor, etc., to get the current that low. For this type of situation, with resistor (or?) you might consider a cheap wall-wort type trickle charger.

25.  Many vehicles have small parasitic drains from clocks, computers, etc.  Failure to keep the battery charged will decrease battery life, possibly by quite a considerable amount.   You should allow for that by proper recharging.

26.  If you test the battery with a real Load Tester every 6 months, or 1 year at the latest, and pay attention to the meter's readings, INCLUDING how fast the voltage drops during the testing, you are unlikely to be ever surprised by battery failure.


Battery prices climbed steeply for awhile, now have steadied, but prices are often quite variable.  Beware, if you want a GENUINE Panasonic battery, because Chinese, etc., 'replicas' are on the market.  Watch the wording in the advertisements.    Be very sure that the battery you purchase, if you want a Panasonic, is going to come as a real genuine Panasonic brand, as some advertising is not very honest.  I have not ...yet ...seen this advertising problem with the Odyssey ...but that would not surprise me.

Panasonic Battery:
Panasonic made small changes in its battery part numbers, and there are several different versions of the battery posts Panasonic offers. The suffix P is the one you probably will prefer. On a genuine Panasonic battery, there are two common posts types.   Sometimes the screw post, which is usable on your Airhead, is cheaper.  Suffixes are AP and P; both will work in an Airhead.  The AP is a vertical threaded post.  The P is a conventional post.  I prefer the conventional post; the wires, to me, fit nicer.  The LC-X1228P is a conventional post (nut and bolt) 28 AH Panasonic battery.  It is 6.57" long x 5.0" wide x 6.97" tall, and 3 pounds heavier (weighs 24 pounds) than the flooded Mareg (of 28 or 30 AH). There is likely a small difference in the maximum height, as measured at the case top (& terminals stick up a wee amount too).  Information on how to deal with the extra height, & your tool tray are earlier in this article you are reading.

Float voltage is OK at 13.5.  Float voltage is not the bike system voltage under alternator charging is a floating voltage for charging during storage, or after overnight SmartCharger use, with the SmartCharger still connected and powered.

Clean & shiny is necessary during the making/tightening of bike wire connections to the battery (and elsewhere's), as teensy voltage drops can upset the voltage regulator, or create other problems.  The larger (28AH) battery, does not generally fit the R65, GS,  /5, ST.  Smaller batteries are 17 to 20 ampere hours usually.  These batteries also fit the classic K bikes, some K bikes can use either size.

VRLA or AGM type batteries come fully charged (if fresh) but I suggest that you check the charge & put a trickle charger on it for the time necessary to have terminal voltage show a full charge, before starting the engine.

All batteries:
No matter what brand you get, be sure that the negative & positive terminals are on the correct side and correct left-right. That avoids wire strain and battery terminal strain, which can reflect back inside the battery, and eventually crack/break the innards connection(s); and, cause other ills.
The self-discharge rate is quite low when the battery is new, so even if the battery sat for 3 months, it is probably still nearly fully charged. Probably sits around 12.5-12.7 Volts.  If under 12.5, be sure to recharge it slowly.

Odyssey battery:
These are made in many sizes, two of which fit all Airheads.   I can recommend the metal-cased version of these batteries for the longest possible life, but at a considerable cost increase, and probably not worth it.   I recommend that the voltage regulator be carefully adjusted on the motorcycle to obtain maximum performance and life for the battery. Further, I recommend that if the motorcycle is not operated often enough to keep the battery at close to 100% of charge, that either a proper Smart Charger be used ...or a small ~1 ampere non-smart type be used ...and for that type of charger, monitor the battery voltage, and shut the charger off when the terminal voltage reaches 14.7, but not over 14.9.  Snowbum had bikes that wer not driven more than once every month or even three months.  He recharged the Odyssey's with a 1 ampere unregulated wall-wart cheapo charger, once every month or two, to 14.7 to 14.9 volts.  It seldom takes more than a short time, perhaps 1-1/2 hours, to reach that level;   The recharging takes care of battery self-discharge & minor drains such as clock, etc.

Do an Internet search for whatever type of battery you intend on purchasing.  Always check for shipping charges and taxes.  Be sure you are getting the actual brand, size and terminals, etc., that you want.

I have eliminated my previous lengthy specific recommendations on where to buy specific batteries and what models... due to being unable to keep up with changes.  Do your own research on the Internet.  I will, however, mention some few sources.

Ted Porter's Beemershop:   Ted likes the Odyssey & also sealed Interstate batteries, such as models FAYIX30L & FAYTX20HL ...and get the plastic support plate.   (831) 438-1100.   34 Janis Way #E, Scotts Valley, CA  open Tuesday through Saturday.  Very knowledgeable BMW folks here.

Tom Cutter's Rubber Chicken Racing Garage: Tom likes the MotoBatt batteries, & stocks and sells those.   1360 Colony Way, Yardley, PA  19067  215-321-7944.  Very knowledgeable BMW guy.

Some have used 'Garden tools' batteries.  Be careful with flooded types, as if no overflow/vent tube, the fumes from the caps vents WILL rot out your steel pan seat, mess with electronics, etc., over many years.   The typical garden battery size being used is U-1.  So,  remember, that some sealed garden types will release corrosive gases.

***Avoid  ...any flooded battery without a venting tube.  The short vent tube elbow must exist on flooded batteries to avoid problems.  It is used with a flexible plastic or rubber tube that directs fumes down to the ground, typically near the forward side area of the rear tire.  The stock place BMW to put that tube is good.   Avoid batteries with vented caps; and, avoid any that do not have the venting outlet on the side and near the top area. Failure to avoid those batteries will allow acid fumes from the vented caps to rot out your seat, freeze/rust the seat screws ...etc.

***AVOID ...any battery that has its + and - terminals reversed.  On an Airhead, the + terminal is on the left, as you sit on the bike.  Trying to make your cables reach and fit is a bad idea.  Many problems from folks doing this; including the occasional $$ damage from reversed polarity connections.  In some situations, the side pressures eventually cause acid fumes leakage.

I recommend you do not use golf-cart and similar batteries!

There are a large number of sources.  Be careful about what you purchase.  I can't list all of these sources.  Ask about batteries on such as the Airheads LIST; the K bikes LIST, etc. Watch out for shipping charges.

Voltage regulators for Airheads; adjusting, details, etc:

Be sure that the various connections at the battery, at the diode board, at the alternator, internally at the ignition switch, ...etc ...are all tight & good, and there are no voltage drops that are excessive!  It does no good to adjust the VR, if these things are poor.

If you have rubber mounts on the diode board, to change them to aftermarket solid metal ones before adjusting the regulator. PIA to install, but a really good idea.  Add the extra grounding wires too.   Motorrad Elektrik, Thunderchild, & Euromotoelectrics sell metal mounts.   My preference is for round, not hexagon, metal mounts ...due to possible interferences.

Measure only at the battery terminals themselves. If you have a dash voltmeter you are probably going to want to have a reference, so do note what it reads in comparison to the digital voltmeter you are using at the battery, probably the dash voltmeter reads 0.3 volt less, and you can do this with engine off but headlight on; and repeat, engine running.  Be sure that your grounds, cables, brushes, wiring inside the timing chest, etc. ...are all properly tight and all grounds properly grounded and secure ...before adjusting the regulator. Be sure you do these things!   Refer to in this website for considerably more information.

At room temperature of the VR case, which means quite soon after engine start, use 14.2-14.3 volts for the VR setting as a decent compromise, using enough rpm.  Up to but not exceeding 14.9 is OK for the Panasonic or Odyssey battery, but lamps life will slightly suffer and battery life can suffer some in hot weather areas ...but 13.9 and under is also a bad idea.  You hardly gain anything by going over 14.5 volts.  I think the best compromise is about 14.3 to 14.5 volts. As soon as the engine warms, the heat rises into the regulator causing the voltage to go down a tenth or two, so do checks and any adjustment before heat develops. I start from a cool engine & adjust the regulator after a 1 or 2 minute engine warm-up, which is enough warmup to allow me to go to 4000 rpm or so.  sells adjustable regulators very reasonably priced; so does

Setting the regulator without knowing that all is OK ...wiring, mounts, diode board, connections, grounding ...etc. truly a waste of your time.

Never, ever ....unless you have an EnDuraLast permanent magnet alternator conversion ....remove an Airhead timing chest outer cover without first disconnecting the battery, typically by just removing all the wires at the negative post.  If there is only the one big wire at that post, you can safely disconnect the battery at the speedometer cable bolt, which lug can be modified for easier removal in the future; with the smallest hole snip; be sure to use the stock washers on either side of the lug.  Failure to disconnect the battery will or could result in a burned diode board.   You will also certainly want a disconnected battery if replacing the diode board mounts.


Do see all prior comments earlier in this article about chargers, including desulfation modes, etc.

There is nothing wrong with using a common battery charger, non-smart type, if used properly.  This applies to any of the battery types:  absorbed mat (AGM) (also called Valve Regulated...VRLA), flooded (slosh), sealed, lithium, etc.   Non-smart type chargers can often be had quite cheaply.  They are adequate for many of you.   Use a common low output non-smart type once every month or two, for just enough time to recharge the battery, but do monitor the voltage!

I do not like Smart Chargers left on for many months, but we all know many will do that, and their manufacturer's tend to push the idea.  I prefer them to be used, perhaps overnight, once every 1 to 3 months, on the AGM/VRLA/Lithium types, & maybe monthly on the flooded types, especially if the bike has small drains, such as from a clock, or weather is hot.

Money-saving hints!     I haven't the foggiest idea why many do not know of this.    You may already own a small to modest sized charger that is non-smart, and is not normally to be left connected and powered for extended periods.   This type of charger, say up to 12 ampere rating (most are around 1 to 3 amperes for motorcycles), can be quite adequately used to maintain a battery over the Winter, when the motorcycle is not being used.  Simply connect it to the bike battery and then put a common cheap timer on the power plug.  Set the timer for a short time period and perhaps for once a week; otherwise, perhaps a few minutes once a day ...or every few days.  Do check now and then that the timer still works and the charging is not too much, not too little (voltmeter)!  If you do not use a timer, just connect the non-smart charger once a month for an hour. Just how long to have it powered and connected depends on the type of battery, and the charger; and your monitoring of of the voltage at the battery terminals. Keep in mind what I said earlier in this article about self-discharge rates for the various types of batteries.

Another way, to use the non-smart inexpensive type of charger to add a series resistor or proper lamp used as a series resistor, in the charger battery lead (either lead, + or -, will do) so that the long-term charging does not exceed 0.060 ampere. No timer needed, just leave it all connected all the time.  You can leave it on darn near forever at 0.020 to 0.060 ampere.  Do check the battery terminal voltage for all methods, before & during the charging.  If the battery is a flooded type, be sure to check the fluid level occasionally (do not forget ...I have mine on my calendar).  Keep the lead-acid battery somewhere's around 13. volts, but this is hardly critical.

Smart chargers are called smart because most of them recharge a battery first to a reasonably proper higher initial voltage.   That higher voltage (which they may call initialization, not the same as my use of the term in this article for preparing a new flooded battery for use) is needed to recharge the battery fully. Once that voltage is reached they automatically drop the charging voltage to one or even two lower levels, the final level is usually called the float level or maintenance level of charging ...which is just enough to maintain the charged condition; and that might be around 12.7 volts, some use higher. Some Smart Chargers have other modes for de-sulfation, perhaps a pulse mode, and some have a final low level.   As noted much earlier in this long article, beware of de-sulfation mode use.

A true Smart Charger is ...or can be ...the best charger for you, but are not necessarily. Do you really (?) want several versions, if you have several types of batteries?  Super-smart-chargers have constant current and constant voltage modes, that are the very best, if the voltages they use are properly selected by the maker.  However, you need not purchase a fancy smart charger.   Understand that occasional use for awhile of any trickle charger or even a modest output charger, may do very well!  There are a few Smart Chargers that can be set to specifically work with various types of batteries.  I have not yet seen any that are really good at doing this automatically, only by setting for such manually.

The truth is that constant very long-term use of a Smart-Charger can somewhat reduce the life of the battery.  That is not what the charger makers say, but it is the truth.  The bottom-line is that once or twice monthly use of any smart charger, perhaps overnight or half a day, depending on type of charger and battery, will almost always keep the battery in reasonably good condition.  I am not against smart chargers, I own some and use them (as well as non-smart types).

An AGM/VRLA such as the Odyssey or Panasonic might only need the charger every 2 to 3 months ...but do not fail to consider any clocks or other small drains ...they do add up!  The biggest advantage of a Smart Charger is that you can connect and plug it in, and pretty much forget about it until Spring arrives; although that is not the best way to use them, and can injure the battery some, especially if the smart charger output is high enough to cause appreciable water loss on a flooded battery; and it is not all that good for the AGM and other types either. The damage to flooded batteries is low, unless the battery fluid level is below the top of the plates.   You really need to check the water level now and then, and maybe the terminal voltage, no matter what type of charger, on a flooded battery. If the water level is below the tops of the plates add only a modest amount such as to just cover the plates. Charge the battery and monitor the fluid level. This is because a heavily discharged flooded battery absorbs the acid-water mixture, and the level might rise during charging to a higher liquid level than you want. Re-adjust the liquid level with distilled water during the charging.

The self-discharge effect is more important in quite hot weather.   All batteries lose charge by themselves, with nothing connected to them.  The self-discharge rate of all batteries rises with temperature rise.  You cannot expect full life out of a premium battery like the Odyssey if you store the battery where it is over 90F for many months; no matter the advertising.  The Odyssey is good at having a low self-discharge; so is the Panasonic.  Most all VRLA, AGM, and BMW GEL batteries are good at having a low self-discharge ...but the rate of self-discharge rises with battery aging!

Once in a great while someone asks about what to do if the bike is stored for a few years.  Best would be to sell or give away the battery.  I used to have a second-best, to put it into your refrigerator (not freezer) and charge it every 6 months to yearly if you could. I have decided that is not so good.  So, my present second-best is to fill to highest level line or even a bit more, with distilled water (if a flooded type that can have water added); then connect a cheap non-smart wal-wort low current charger to it, with a series resistor to limit the current flow to 0.060 ampere, as measured after a full charge ...and keep it in relatively cool place.  The liquid level will probably be OK for a very long time.  If you have access, you could just recharge the battery occasionally during the long term storage.   If you want the easiest thing to do, just connect a Smart Charger constantly, but battery life will suffer some, and on flooded batteries, the fluid level WILL decrease.

Smart Chargers vary considerably in design.   Some designs have features that can cause confusion and/or problems.    Most smart chargers will have no output, therefore no charging ...unless the battery they are connected to has at least some voltage (maybe 8v or greater??).  I have used a figure of 10 volts, earlier in this article.   If your battery is drained very considerably, or is dead, and your Smart Charger does not begin to charge that battery, you have no choice but to use some other type of charger on that battery (or jumper to another battery for a few seconds), until the battery terminal voltage rises enough for the Smart Charger to then be connected, recognize the battery, and turn itself on.  Of course, the battery could be no good, but it will not hurt to try a conventional charger on the battery for awhile.   It usually takes only seconds of any other type of charger, even a momentary connection to a car battery put just enough of a charge into your bike's battery to allow it to trigger a Smart Charger connected almost immediately afterwards.   This is not to be done with lithium batteries.

Beware of de-sulfation chargers!  This is especially so on Can-bus bikes, but also on any bike with electronics.  Do not use de-sulfating mode on lithium batteries!

Miscl. section:

For riders that commute in cities with stop and go traffic such that the electrical system does not keep the battery charged, and you want to connect a battery charger every night, you really should have a Smart Charger, with an easy to connect setup.  Some have an SAE type polarized two-wire connector fastened semi-permanently to the battery.  While that can be OK, you want to be cautious about wear, fires, etc.   I suggest using a BMW DIN (sometimes called Hella) accessory plug on the charger and plugging it into a DIN socket mounted someplace convenient.  Many early model Airheads, and many later models, both as stock items, came with the DIN type socket, mounted on a small bracket that is often located near the top of the left side rear shock absorber unit.  DIN sockets and DIN work well & don't have the failure of common American type cigarette sockets/plugs of disconnecting or making poor contact.  Make sure there is a fuse in the + lead of the socket. The stock size fuse was 8 amperes, but up to 16 amperes can be used if you use the socket for other purposes needing more current.

I caution that the socket should be wired so its negative lead (usually black) is connected to the frame and not to the battery negative post. The reason is due to possibly grounding the battery without the battery ground wire at the speedometer bolt being connected, after you have purposely disconnected it.  If the socket itself grounded to the frame, and was also connected to the battery negative post, then the battery would be grounded when you want it disconnected.  That can cause shorts or sparks and burned-up diode board type problems when removing and reinstalling the front cover of an Airhead. Because of that, I recommend the grounding wire from the accessory outlet should be connected to the frame, perhaps near the ignition coil....but that can vary depending on your model of Airhead, etc.

As a general rule, the largest size of battery charger that might be used at any time, safely, with your Airhead's battery is one rated at 12 amperes. One as small as 1/4th ampere is often OK ...but not always, if the battery is deeply discharged. Nearly all 6 to 12 ampere rated chargers can be safely used on a lead-acid bike battery rated over approximately 10AH. Using chargers rated over 12 amps, things may get iffy, but some chargers even as high as 20 ampere rated are OK for temporary recharging.  The reason they are probably OK is because while they start off with a moderately high ampere charge, they very quickly taper off, within a few minutes.

A charger that is too small may not fully recharge the battery if it is well-drained from a day's commuting and you use the bike again the next morning. Many small non-smart motorcycle type chargers are rated at 0.5 to 2 amperes. Do not expect them to necessarily supply their rated current, often not very close to it, for your battery, especially for very long. Most of the various types of chargers, especially the cheaper black-box types, that we call a 'wall-warts', plug directly without a cord into your wall socket, & have a built in over-current circuit breaker, that tends to constantly recycle if the battery charge level is quite low ...or a cell or two are somewhat, or more than somewhat failing.  These wal-warts tend to fail from that sort of recycling usage.  It really is best to get a proper sized Smart Charger for commuters usage.   I have thought about the size needed for the Airheads, and I think one rated at 3 amperes or more would be fine for anyone, and one rated at 2 amperes would do for most, possibly even somewhat lower.

There are, or can be, important problems with large size standard non-smart; that is, old-fashioned chargers. Depending on the particular design, they might tend to overcharge the battery if left turned on for too long. It is not the current output capability that causes this (at least up to the 10, sometimes the 12 or even 20 ampere size), but the internal resistance of the charger is lower, and so the output voltage also tends, by design, to be a bit higher under actual use, thus this type of charger tends to overcharge. Not all will do this.  I think 30% of battery capacity in ampere-hours, is OK as a maximum number of amperes on the charger's meter, for the initial few minutes of charging, is OK. Thus, if you have a 30 AH battery, you can safely start charging at as much as 9 amperes, which should taper off fast ...within a few minutes.

I think that owning a 6 to 12 ampere charger is very useful for bike batteries. I have tested some 20 amp chargers that would charge a well-discharged bike battery at 12 to 15 amperes, and within two minutes taper off a whole lot, perhaps to a few amperes, no damage being done. If one does not taper off quickly, do not use it! Some old-fashioned simple chargers are designed such that their output current does not taper off enough, as the battery terminal voltage rises from the charging.  I have a 10/12 ampere charger that works fine. Mine has an adjustable timer on it, a handy feature. If I connect this charger to one of my Airheads in my garage that has a flooded type battery, once a month, it shows a 6 ampere charge for less than a minute, & is down to 4 amperes within three minutes, then slowly tapers to under 1 ampere as the battery is recharged. That type of operation is perfectly OK.  You don't want 6 or more amperes of charging for hours, but minutes is OK. Even half an hour or sometimes a full hour is probably OK if the battery does not warm up much. Don't allow the battery voltage to be excessive at any time.

For the Odyssey brand of battery, you can initialize at up to 50% of AH rating per Odyssey; but I say 40% maximum, and 30% is better as a maximum.

An absorbed mat battery (AGM or VRLA) (WestCo/Panasonic/Digi-Key/Yuasa...ETC.) will USUALLY recharge far more quickly than a flooded type, as its internal self-discharge was much lower so the % charge loss is less; and the ability to more fully use the higher charging current is better. A Smart Charger might take overnight for any type, depending on the ampere rating & design of the Smart Charger. Smart Chargers are worthwhile, if you know the limitations.

IF you use a common, non-smart charger, do monitor the battery voltage. When the voltage reaches the fully charged amount, turn the charger off. Don't allow the battery to get much over baby bottle warmth.

The rule-of-thumb that a battery should not be charged at a rate over 10% of its ampere-hour rating is a good rule, but not a strict one; as 15% is usually fine, and even twice that for short periods. What they don't usually tell you is that the so-called 10% rule is for 'continuous'.   If your battery charger is still delivering 3 or more amperes & the terminal voltage of the battery is already over 14.2, then you want to be cautious about using that charger, and certainly not allow the voltage to get too high.

The use of old-fashioned service station quick chargers (typically 70 amperes & higher) is absolutely forbidden on bike batteries ...and is not good for large car batteries either. Huge charging currents will cause spot heating in the battery, and such things as plate buckling, steam, etc., are likely....& quite possibly the battery will be destroyed.

Excessive charging, over a long period of time, even if the excess charging is of a rather low level, will slowly cause oxidation of the inter-cell connections, eating them away, reducing battery life. The end result is a cracked inter-cell connector, and a catastrophic sudden failure to start the bike, yet lights might be OK. This failure cause is very much unknown for whatever reason. This is part of the reason for not leaving a Smart Charger connected & powered for years, during extended storage, & even 1 year is sometimes damaging. That is why a constant current at not over 0.060 ampere is better (after a full charge).  Many problems with sudden failures of AGM/VRLA batteries have come from people leaving them for long periods of time on Smart Chargers.  Naturally, the makers and sellers do not want you to know this. However, battery life decreases if not kept fully charged.

DE-SULFATION, knowing about it more in-depth:

Usually when a lead-acid battery is quite well-sulfated, from age or being discharged for a long time, the battery is no good, & cannot be 'fixed'. There are exceptions. If you want to try to de-sulfate a battery, you can try by discharging it, if not already, to about 10.3 to 10.5 volts (the Odyssey type maybe much lower). Then, recharge with a substantial sized charger, to around 14.7 volts at room temperature.   The charger should be at least 6 ampere rating, but not over 20. Some chargers are advertised as having pulse modes or similar, & that they will de-sulfate even a quite bad battery. This can be partially true. The pulse mode is better, but not worth a premium. Use of the higher ampere rated charger the way described in this paragraph will probably help a sulfated battery more than a much lower de-sulfation mode in a Smart Charger. This will be denied by those trying to sell Smart Chargers. Still, the best method is the one described by me much earlier ....which is very different, and uses a very low current charging.  I, again, caution you to not use de-sulfation charge modes on Can-bus nor Airheads, unless the battery is DISCONNECTED can damage the electrical system.

Practical advice for battery voltages for charging & float charging:

Before getting into the practical advice, I will share with you the official chart for flooded lead-acid battery charge, electrolyte specific gravity, and open circuit voltage.  Conditions are for a vehicle starting type of battery containing antimony in the plates.  Readings are at 26C (78.8F).   The battery rested for 24 hours after charge or discharge; voltages are then measured.

You will be unable to measure Specific Gravity of battery fluid (electrolyte) unless you have the flooded type with removal caps.

Approximate state of charge

**Average Specific Gravity

Open Circuit Voltage After resting
















Although I have given you rather specific advice in this long article on various voltages, the following is practical advice, since voltage regulators on the various motorcycles will vary considerably ...or, you may want to know what is practical for setting yours if it is adjustable.   You might be interested in what settings are practical and useful for the three major battery types; and, a few other things.

If the battery and voltage regulator are both at "~room temperature" (70F approximately), then I would be OK with you setting your VR for 14.1-14.4 volts (before the engine heats up the VR).  This will probably result in a longer battery life, and only quite slightly less life for your incandescent lamps, which will be a wee bit brighter while going down the road.   On a really practical basis, ANY of these batteries will be reasonably OK with the motorcycle voltage regulator set for 13.8 to 14.5 volts under most any temperature you measure the battery at.   The lower portion of that range may not give you the best life from the battery.

In all situations, all types of lead-acid batteries:  after a battery is charged, and the charger disconnected ...and this also applies to after the engine is shut off; ....after a few hours of nothing connected as a load but maybe a clock, the battery should be ~12.6 volts.  If the battery/bike has been sitting for some days, etc. ...then, if under 12.5, be sure to recharge the battery.

Additional information....and somewhat different viewpoint, etc:
I do not agree 100% with Anton, but I recommend reading it, and my nitpicks are hardly worth mentioning.

Load Tests:
Load Testing is the best way to determine battery condition ...on any type of battery. However, there are some finer points of doing the testing, that will reveal lots more than just the tester maker's information.

Simple voltage testing a battery to determine charge/condition; or, using a hydrometer on a flooded type battery for the same purpose, are NOT reliable checks on battery condition.   One of several reasons is that the battery could seem to charge up perfectly OK, ...and you might even check for correct voltage; and, let us assume that is fine ...and yet you have almost no output to run a load like a starter, sometimes even for a headlight, ...all because an inter-cell connection was seriously cracked or corroded away internally, as described earlier herein.  This is fairly common; as is sulfation, which can have little to no effect on voltage without a known load.  This are just two of the possible problems if you only check the voltage or only hydrometer check, ...or both.   True load testing is a far better method of determining battery condition, as a load tester measures current output and voltage, both with a substantial real and known value of load , over a known period of time (typically 15 seconds).  A load testing done while watching the RATE of voltage lowering adds a LOT of information, and, while unknown, I will explain that, etc.

A slightly better total method is a capacity test, but is not likely going to be what you do ...and is almost never really needed. It also requires costly equipment. There are other types of tests, all requiring costly equipment.   A very sophisticated type of battery tester that measures conductance/impedance is available, these testers are hundreds to thousands of dollars.  They measure using a complicated formula used in conjunction with passing both low frequency A.C. and D.C. through the battery.    They are not further discussed here ...besides to tell you that they are absolutely not needed for your bike, car, truck, etc.

Regarding load testing of the battery, voltage drop while cranking, etc.:
You can use a digital voltmeter at the battery, & the motorcycle's starter motor, to perform a load test, with a very approximate resulting guess of the battery condition.  Testing this way depends on the condition of the starter, the temperature of the engine, starter, battery; even the oil grade and if a high compression engine or not ...etc. The colder the temperature, the lower the voltage, due to higher current drains caused by increased friction and other losses, and the slower chemical activity of the battery.  Cold weather tests are also more demanding on the battery.  A problem with this type of test is whether or not you do, or even could, know the real condition and ampere draw of the starter motor, and condition of peripherals like the solenoid switch, wiring, etc. See item #1, below.

Load testers were traditionally only used by automotive service centers and sometimes available at places that sold batteries.  The availability of a load test by these types of businesses is still relatively common, and often is free.  However, you really should be knowledgeable about how the test is done, and what the readings or interpretations mean.  You don't have to take your battery someplace, nor depend on someone who might be more interested in selling you a battery.....if you own your own relatively inexpensive load tester.   Harbor Freight Company sells two types, a 100 ampere type and a larger 2-meters higher current type, and both of these are quite good for the low price, are often on sale ...and they do work well.  I particularly like the two-meter larger one, I think it is much more versatile ....and more accurate ....and you can use it on your car or truck battery, not just a motorcycle battery.

1.  If you do not use a formal Load Tester, the following is a quickie way of doing load-testing, and it is a "sort-of-adequate" method:

It just so happens that the typical Airhead starter motor current drain, with a good starter, on a mild day, is going to average approximately 60-100 amperes during cranking; but considerably more when first starting the rotation of the engine; especially if the engine is cold, perhaps from an overnight storage. That means that the starter itself can be used as decent-enough load ...assuming the starter motor is OK, & same for connections & wires.  Remove the fuel (emptying the fuel bowls on Airheads is a good method), or disable the ignition (ground spark plug caps properly or disconnect coil primary) from the engine so the engine will not start. Be careful what method you use for the particular make & model of motorcycle.   First charge the battery fully while monitoring the battery terminal voltage. Disconnect the charger & let the battery sit for an hour or three.   If you think the battery is fully charged & does not need charging first, at least check the voltage first.  Connect a voltmeter (digital type) directly to the battery terminals.  Crank the engine for 10 to 15 measured seconds.  At the end of that time period, while still cranking, note the voltage, and see the voltage readings below. You must measure the voltage at the battery terminals themselves.  Do not measure at any connection fastened to those terminals, or from frame, etc.  DURING the cranking, also watch the voltage. If if sags slowly more than half a volt, the battery is failing.

2.  If you do use a Load Tester:  load tests on batteries are done at approximately three times the battery capacity in AH. Thus, a decent load test is done at about 90 amperes on a 30 AH battery.   The literature with the Load Tester will have more information.  Some literature, for some types of batteries, will show that the testing current should be 1/2 of CCA.  That is a more critical and I believe much more accurate type of test and you can interpret it to give you a rather good idea of the amount of life left in the battery. The regular type of test should last 10 to 15 measured seconds.  The 2-meters Harbor Freight unit is semi-automatic ...and has fully and continuously adjustable load settings and a bell to tell you when the time is up; just quickly dial up the test level of current, then watch and let the unit do the automatic testing.  For future use, just leave the adjustor knob in the same position, and you will be able to attach the jumper cables and the unit immediately starts the test.  Remove the cables when the test is completed.  Be sure to watch the voltmeter during the test.  Sagging more than 0.4 or 0.5 volt means a battery has aged considerably.

3.  For either 1 or 2, above:
Semi-officially, a good battery supposedly will show the following voltages during the test at the 10 to 15 second point, and the temperature shown below is that of the battery just prior to testing:
9.8 volts or higher at 70F
9.5 volts or higher at 50F
8.7 or 8.8 volts or higher at 0F.
A fair condition battery will show a few tenths less, and a top-notch battery will show CONSIDERABLY higher.  The digital voltmeter should be connected to the battery terminal posts, not to any wires or connectors connected to those posts.  This will avoid slight voltage differences.    I consider the voltages, above, to be too high, and I tend to watch the voltage SAG closely.

NOTE!   Load Testers that are reasonably priced, such as the Harbor Freight unit, have a voltmeter built-in, or at least good-bad indication of some sort; and the way they do the voltage measurement is "OK".  Do the test at 1/2 the rated CCA instead of 3 times the AH rating, and if the voltage needle, after maybe 5 seconds, stabilizes quite well, and does not continue to drift more than 0.2 volt downwards, yet the needle is still well into the green good category, the battery is likely in excellent condition.     I recommend you use an accurate digital voltmeter at the battery terminals to compare to the load tester's analog meter, for more accurate information. You will probably find that the readings agree well-enough. If they do not....use the small meter adjusting screw on the Harbor Freight meter face to reset the meter needle slightly (it will then be off-zero).  The testing should always be done with the Harbor Freight analog meter in the same horizontal or vertical position, to eliminate meter needle mechanical balance irregularities.  If you want to adjust the Harbor Freight meter face a bit more accurately, follow this advice:

Rotate the Harbor Freight two-meter type unit's load adjustment to sufficiently off, so no load will be applied.  Connect the Harbor Freight unit to the battery via its big alligator clamps.  Set the Harbor Freight unit either standing up or the back is flat downwards,  whichever position you intend to use, & so indicate it on the Tester, so you will always use it.  Connect your accurate digital voltmeter to the Harbor Freight units big alligator clamps.  Adjust the Harbor Freight unit's meter (slotted screw on the face of the meter) so it reads the same as the digital meter.   That's all there is to this.

Starting problems?   Try this:

initial upload 02/04/2003 and initial copyright.
03/04/2005:  Update entire article to reflect latest information and include all prior revisions, greatly expand information.
04/13/2005:  Note, on Advanced, possibly raising prices.
05/03/2005:  Remove all information on company, due to non-responsiveness.
11/26/2005:  Update entire article.
11/29/2005:  Update digikey shipping information.
02/13/2006:  Add information on WestCo's BB brand.
03/02/2006:  Update on Digikey.
12/20/2006:  Re-edit entire article.
03/21/2007:  Expand upon charging efficiencies and self discharge losses.
04/15/2007:  Additional information on Yuasa and also garden type batteries.
10/30/2008:  Remove pricing and methods of purchasing from Digikey, update a few other places (minor).
03/31/2009:  Update the article entirely, clarifying some things, reducing ugly color changes, etc.
06/05/2009:  Modest updates for clarity and add information on load testing and change title slightly to accommodate that.
03/30/2010:  Clean up appearance; make minor updates for clarity.
07/21/2010:  Add practical advice on voltages section.
03/03/2011:  Clean up article, add emphasis, straighten out confusion on voltages.
06/11/2012:  Clarify details, update for Odyssey somewhat more, etc.
10/11/2012:  Add QR code, add language button, update Google Ad-Sense code
12/19/2012:  Slight updating on AGM batteries regarding % of vehicle use.  Expand slightly on conductance/impedance & minor other areas.
01/08/2013:  Clean up slightly, add a bit more on nerdy stuff to know.  Still a messy article. 
03/09/2013   Clean up a bit more; clarify a few details; add information on timer usage.
03/19/2013:  Revise and simplify the load testing procedure(s).
05/19/2013:  Clean up article quite a bit, also remove a lot of old outdated battery information.
05/22/2013:  Update the lithium battery information, condense it.
10/29/2013:  Update for clarity, add more cautions & information on DEsulfation mode problems.
12/14/2013:  More information on voltages, clean up article, add standard voltage information, clarify details.
04/27/2014:  Add note regarding poor battery and voltmeter swinging.
05/19/2014:  Update with more information on sulfation and rejuvenation.
11/17/2014:  Add note on purchasing batteries at very top area.
12/22/2014:  Add section on battery type descriptions at the top, from hosting on the Airheads LIST.
12/26/2014:   Minor tech changes.  Finish re-arranging the article, eliminating some redundancies, etc.
12/27/2014+:  Due to misunderstanding about battery capacity in A-H, in the area about small capacity Lithium batteries, I revised that section.  Slight update later this same day. Further small updates were done as I obtained more information, particularly on LiFePO4 types, on 03/01/2015 & 03/17/2015.
08/12/2015 and 08/28/2015:   Due to confusion, added more information & strict advice on Lithium batteries.
01/18/2016:  Updated the entire article.  Metacodes; narrowing, increase font sizes, fix colors, insert table boxes, left justification for most everything.  Still overly long and could use quite a bit of shortening.
03/09/2016:  Update meta-codes; layout, fonts, colors, clarifications, some simplifications, some redundancies. 
03/10/2016:  Fix so looks OK on IE and Chrome, as had some superfluous hidden tags.
09/16/2016:  Update metacodes, scripts, layout, content improvements for clarity.
10/02/2017:  Some improvement in clarity, and a bit on color reduction.  Not a complete upgrading.
10/12/2017:  Substantial revision. Improve clarity of explanations. Reduce fonts and color changes.  Clean up article.
02/28/2018:  Minor fixes to spacing, underlines, layout...mostly appearance things.
07/06/2018:  Revise section on battery sources.
03/07/2019:  Minor cleanup and minor clarifications.
01/01/2020:  Clean-up discussion about lithium batteries to improve ease of understanding.
12/27/2022:  Minor updates.  NOT a full article go-through.
12/29/2022:  Slight update on Lithium batteries, and, add red box details on my LiFePO4 rejuvenation services.   Again, 07/19/2023.

Copyright 2023, R. Fleischer

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Last check/edit: Tuesday, July 18, 2023