David Hough recently published an article in ON re chargers for modern batteries.

His excellent article did not mention a very common, inexpensive charger sold by many bike shops, including some BMW dealers, that is used by some of us.

It is the YUASA 12V900 that carries model designation VM12990-02 near its electrical spec info and retails for less than $40. It rated up to 900 mA (0.9 A) so makes a good maintenance charger but wouldn't be correct choice for charging flat batteries where 5-7 A is more appropriate.

I allowed the OEM BMW gel cell in my 08 RT to sit in the bike not connected to the YUASA for 5 days, then measured the battery voltage using my Fluke. It was 12.86 V. When connected to the YUASA charger, voltage quickly climbed to 14.3 V and briefly flickered to about 14.6 at the battery terminal, all in under 30 seconds, then as rapidly decreased to 13.25 V at which point the charger switched to STORAGE (float) mode as shown by its indicator lights. Shows that my battery doesn't lose much charge in a few days and that the charger maintains a reasonable float level, though perhaps a fraction of a V lower than some others. Charge capacity is NOT at all linear with voltage so the small difference is meaningless for practical purposes. Its clear the YUASA does OEM gel cell maintenance just fine.

I don't happen to have a bike-size Odyssey to test on- they're worst case for charger voltage of types currently used but might someday replace my OEM battery with one- I've had excellent performance from them in my auto track machinery. They hold a charge way longer than other stuff when not in use and have a lot of cranking punch for their rated capacity. But they absolutely require a suitable charger- all your old ones in the garage from the days of fillable batteries WILL be worthless unless you happen to have one meant for the non-fillable maintenance free batteries of the late 1970s, etc that had Cd in the plates- chargers meant for those deliver enough voltage to charge an AGM like the Odyssey though they lack automatic shutoff and the sophistication of modern, solid state controlled chargers than can d-sulfate plates and do other cute "rejuvenating" tricks.