Check out the Optimate 4 Dual Program. It has a mode specifically for charging a BMW over the CANBUS. And a mode for charging regular batteries.
If you go with a Battery Tender, you might want to go with the Battery Tender Junior. It has a lower maximum current than the regular BT. The regular BT, can, under certain conditions, supply too much charging current and F up a gel battery.
'09 R12GS, '05 GSX-R1000
Iron Butt # 4999, WERA/CCS EX # 666 (currently, expired), AMA Life Member
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