I recently bought a 2005 R1200RT and am new to the bike. On my 1996 R1100RT I could plug my BMW Brand charger in to the accessory port to keep the battery fresh. When I do this with the 1200 it does not take the charge. The port works for my GPS when the bike is turned on. Is there some better/different way to attach the charger? Do I have to do th pigtail thing direct to the battery?