heh good question. quite possibly they list horsepower in Kw also. So like 110w, max. With 25w for charging, and originally 25w for original headlight, and about 40-50w or so for ignition, i think, yeah- you're about break even on alternator power. Most of the batteries current is going to go towards pushing the starter motor, unless you add gizmos and bigger lights. With your big headlight, I suspect you're constantly stressing the system. I'm curious about your "neutral" setting on the switch, as well, and am trying to follow the wiring to see what it connects and where, to find out what it does. Weird. Sorr yIm no real help, I only am familiar and only partly at that with the BMW charging systems, but I assume they all work generally the same.