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Battery Tech - Battery selection - Sealed batteries - Charging
"My battery is dead and I need a new one. Which one should I buy for my BMW?"
First off, here are the stock BMW batteries:
The long-wheelbase airheads (late /5 onward), K75, K100, and '93 K1100LT (with ABS1) will usually accept either the large (25AH) or small (19AH) BMW battery. These are your choices:
The short wheelbase /5 airheads, early R65, 4-valve K bikes with ABS2, and oilheads are designed to only accept the small (19AH) Mareg battery. Do not believe the old literature that says you should use the YB18! Even Yuasa has dropped this ill-fitting battery from their latest recommendations. It can be made to fit in some cases, but it will never fit well.
| Battery | Height | Length | Width | Notes | |
|---|---|---|---|---|---|
| O E M |
BMW 19AH gel | 6.8" | 7.3" | 3.2" | Slightly taller than flooded |
| BMW 19AH wet | 6.7" | 7.3" | 3.2" | ||
| BMW 25AH wet | 6.7" | 7.3" | 5.05" | Same as 19AH but wider | |
| BMW 14AH wet | R1100S non-ABS | ||||
| Yuasa YTX14-BS | 145mm | 150mm | 87mm | R1200GS/ST, K1200R/S | |
| Yuasa YTZ12S | 110mm | 150mm | 87mm | HP2 | |
| A F T E R M A R K E T |
Yuasa Y60-N24AL-B | 6.7" | 7.2" | 4.9" | Good match for BMW 25AH |
| Yuasa 53030 | 6.9" | 7.4" | 5.1" | Dims taken from literature | |
| Yuasa YB18A-LA | 6.4" | 7.1" * | 3.55" | Too wide for some small trays | |
| Panasonic | Sealed | ||||
| Panasonic 1220 | 6.6" | 7.1" | 3.0" | Sealed | |
| Odyssey PC-545 | Sealed | ||||
| Odyssey PC-680 | Sealed | ||||
*Plus end vent.
There are two main flavors of lead-acid batteries: flooded and sealed.
Flooded (which has free liquid electrolyte, like the OEM batteries) can be standard or low-maintenance.
Sealed (should not be opened, ever) are also in two flavors, AGM (absorptive glass mat) and gel.
Sealed batteries don't have loose, liquid electrolyte (acid) in them; instead, it's absorbed in a thick fiberglass mat and is thus immobilized. This mat looks like fluffy cardboard when it's not in a battery.
The good: there is nothing to spill when the battery tips over, and very little to spill if it cracks.
The bad: with the immobilized acid, the only ion movement is by diffusion. So you can get stratification which leaves part of the plate in a weak acid solution and part in a strong solution. Ideally, all areas would have the same concentration so the entire plate can work for you. Also, cold performance is theoretically worse because of the slow replenishment of ions at the plate surface (they get 'used up' and need to be replaced). IIRC I could start the K75 down to about 5°F with the flooded battery but the sealed one was only good to about 10 or 15.
Due to the chemistry involved, sealed batteries usually have an open-circuit voltage of 13.1 to 13.2 volts, which is probably why they are so famous for eliminating ABS faults (by keeping the voltage higher during cranking). Flooded batteries are usually designed to have a voltage of about 12.6 to 12.8. You can get a flooded battery to maintain a higher voltage but it's not really good for it and performance suffers. With higher voltages, the charging force (difference between the resting voltage and the applied voltage) is smaller and you can get into situations where the battery might not get fully charged. This is kind of complicated but the uncharged portion becomes permanently unusable over time.
Most sealed batteries, but the Westco/Panasonic in specific, seem to want a higher charging voltage than most Beemers put out. The weak recharge power of the Airheads is just an additional factor; even the Oilheads have poor (my observation) success overall with the Westco.
Some people have no problems with it. Many people seem to use supplemental charging and/or set their voltage regulators higher. They were very commonly used in the late 90s as a way to get around the ABS faults that were common with the R1100 bikes, since the sealed battery chemistry has a higher open-circuit voltage (low voltage seemed to be causing the faults). Problem is, that higher OCV means a slightly higher charging voltage is needed and the bikes don't do that. Results were usually great for the first year or so, while the battery got by on its higher OCV, but the faults then came back as the battery failed (due to seldom being fully recharged and eventually getting permanent sulfation - my theory).
This was my opinion before I bought my Oilhead, but my own experience was exactly in line with that. My bike had the Westco installed about a year before I bought it, and from the day I rode away from the PO's house I had nonstop ABS faults (the PO had already told me this was normal for him, too). Recharging the battery might get me one clean start, but that was about it. I became the master of the rolling restart. Eventually the battery died completely (after a whole 3 years of life, max) and I got a BMW battery. I don't think I've gotten a fault since then, but it's only been a year or so.
This is mostly about Oilheads, since that's where the sealed battery tradition really developed. I see no reason for Airheads to have better results. A guy whose Westco died on day #1 of the Big Dog last year recalled that it was his second one to have done so after a very short life. But he got a third one (said he liked them!?!?) since there wasn't a BMW battery ready to go at the dealer.
I have no hard information on this, but it's very likely that other sealed batteries work better. I'm very tempted to try the Odyssey at some point, especially for the race bike. It should work even better against ABS faults, since it's really the voltage drop that is the problem, not the standing voltage. The Odyssey has thinner plates (I think), ergo more plate surface area and less voltage drop under load. If the charging voltage is a good match then you're good to go. I don't have enough information yet to be able to talk about the new BMW sealed battery, although it's very interesting to me that they have switched to the new 'gel' type. To some extent, the designers can work around the voltage issues although I think the sealed batteries will always need more voltage than the flooded ones do. In any case, if you want to run a sealed battery in an Airhead, make sure your charging system is in top shape, get the more aggressive voltage regulator, try to make sure you don't park it with a half-flat battery after running your heated jacket and grips late into the night, etc.
So in summary, sealed batteries are great for what they do - or don't do. The don't leak, which is handy for a bike that might be upside down on short notice. They don't need watering (really, the BMW batteries hardly do either) and they'll keep your ABS faults at bay for a while, especially if you keep the bike on a tender. But the Westco specifically doesn't last very well, and Panasonic has openly stated that they're not recommended for vehicle use.
I do use the BMW gel battery in R1100 models, though, due to the location. The battery is difficult to access and check the electrolyte level on, and on the left side (where the vent tube is on a flooded battery) the main wiring harness runs just under the battery tray. I see a LOT of damage to the wiring harness here, from leaks in the vent hose or vent hoses which have been disconnected. I've even seen cracks in the fuel pipe there from acid leakage, which is a fairly expensive repair. Overall, this is a good application for a sealed battery as the benefits outweigh the price/performance loss.
YMMV, and obviously many are happy with their Westcos and other sealed batteries. My opinion is based on a lot of feedback (good and bad) from riders combined with a pretty decent understanding of battery electrochemistry. I'm sure many are better than Westco, and this market is developing constantly. For now, I can get sealed batteries for free but I buy BMW batteries instead.
Because sealed batteries have advantages, as long as the battery design matches the bike properly. Especially on newer bikes where the battery is hidden beneath the fairing and maybe even the gas tank, a maintenance-free design is desirable.
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