Panasonic Battery Upgrade
Maybe I worry too much, but I always imagine the worst when the GS tips over onto a cylinder head and the electrolyte in the battery starts sloshing around. The vent tube is routed low enough so that any acid that does manage to escape should make it to the ground without splashing on anything metal, but there's always the chance that won't go according to plan. And regular maintenance of the electrolyte level is also necessary to keep the battery in good shape. That's not a big deal, since removing the battery is pretty easy on the GS. But it's just one more thing to screw around with, and there are ways of keeping things simple when it comes to batteries. Frankly I was surprised when I checked the log for the R100GS and found that the BMW battery was almost six years old, as it had given no signs of ageing like slow cranking or unexpectedly going flat. But six years is plenty for any battery, and I'd just as soon replace it in the comfort of my own garage than have to bump start the bike somewhere out on the road until I can find something that would fit. I'd had pretty good luck with a Panasonic sealed battery in the K1200RS, and with Digi-Key's $58 and change price (including shipping), swapping out the wet cell BMW battery for the maintenance free Panasonic was a no brainer. A week after the check went in the mail to Digi-Key, the Panasonic was sitting on the door step.
 As shown by the part number on the side of the box, the correct battery for the R100GS is an LC-X1228P, the P referring to the terminal type. We want flat lugs with bolt holes, ideally with positive and negative positioned just like the OEM battery, and that's what we get with this Panasonic. They call it a VRLA battery, short for valve-regulated lead-acid, and it uses AGM (Absorbed Glass Mat) technology to eliminate the liquid electrolyte. The LC-X1228P is rated at 28 Amp Hours, just like the original. This battery came with a few California specific stickers adhering to the top surface, each of which left a nasty bit of paper and glue behind when I removed them. A little 3M feathering disk adhesive remover took care of the problem, but it also removed some of the printing from the top of the battery and left a hazy surface in place of the shine every where else. Size wise, the Panasonic is about 5/8" short in the long dimension, and about a half inch taller when measured over the terminals.
I found I had to make two alterations to get the Panasonic battery to fit. Since the top surface us just a little taller than the original, I had to grind down the rubber bumper on the bottom of the tool tray so that the saddle  wouldn't rub too much on the top of the tool tray. This turned out to be something of a feature, as I was able to remove just enough material so that the seat pushes on the top of the tool box, keeping the lid in place and preventing it from banging around on rough roads. There turned out to be plenty of room above the electrodes, even though they stick up above the top of the battery case.
This is easy to see in the photo at right, which shows the rear terminal. Visual access is very limited to the front terminal, but I was able to verify that a similar amount of clearance was present by getting my eye into just the right spot.
The second modification was to cut a spacer to take up the front to back slop created by the shorter length dimension of the Panasonic battery. I dug around in the scrap drawer looking for a suitably sized piece of pine, but couldn't find anything big enough. Instead I came up with some oak, which after trimming on the table saw turned out to be just perfect. A coat of paint finished it off and would prevent absorption of grease and road grime.
 Removing the original battery was very straight forward, and consisted of removing the seat and tool tray, disconnecting the wires from positive and negative terminals, unhooking the two rubber battery straps, and lifting out the old battery. Installing the Panasonic was also easy, even easier than the stocker as Panasonic had thoughtfully incorporated finger holds into the top of the battery case that provided excellent purchase when lowering the battery into the tray.
I elected to install the block at the front of the new battery, as this gave more room between the battery and the power distribution panel that lived under the main frame tube. There's also more of the battery box at the front, and this would help the block to stay in place better than the short lip at the back of the 'box. The standard 3/4" thickness of the oak meant that it was a tight fit, but I really didn't want it flopping around and also didn't want to end up gluing it to the battery box to keep it in place.
The photo below also shows that the front battery strap gets a new routing to avoid interfering with the positive battery terminal. The longer path combined with the slightly taller battery to make stretching the strap somewhat of a work out, but with a pair of water pump pliers and a little extra grunt the task was done soon enough. No such problems were encountered for the rear strap, which mounts in the conventional fashion.
The battery had enough charge right out of the box to fire up the bike, and after ensuring that everything was working normally I hooked up a BatteryTender and knocked off for the evening. The next morning the 'Tender showed a green light to indicate that the Panasonic had reached full charge.
Panasonic's spec sheets say that normal life for these AGM wonders are three to six years, depending on charging and temperature. Those with more experience report lives in this range, but add that when the battery quits, failure often comes without warning and attempts to recharge are unsuccessful. But at $58 delivered, the Panasonic costs just over half what a BMW battery does ($95 at this writing), and I don't have to waste time or pay for shipping chasing it down. My way of looking at it is that the Panasonic cost may be a few dollars more than the factory battery, since I'll probably end up replacing it at the start of its fourth riding season to avoid any chance of it going flat on the highway. That's about half the life I got out of the stocker, but the convenience and lack of electrolyte are worth it to me.
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