I just installed an Odyssey PC680 in my R, and have been keeping it plugged into the BMW charger.
According to the Odyssey owner's manual, a trickle charger of 2.0A will keep the battery charged, but will not charge it if it is depleted.
A full charge on the battery is listed as 12.84 volts or higher.
12.50 Volts is a 75% charge
12.18 Volts is a 50% charge
11.88 volts is a 25% charge.
The manual lists the Odyssey website url
http://www.odysseyfactory.com/odycharg_c.htm
which has a list of suitable chargers, headed by Odyssey chargers of course.
During my installation the positive lead reached to the new battery o.k., the negative lead was short; I purchased a 12" extension, 2 eye loops, at Napa for about $6.
Bike starts a whole lot better now.
