Originally Posted by lucid
So the various experiences reported in this thread demonstrate a diverse set of outcomes, and it sounds like different driving patterns and cars (configuration and maybe software) limit our ability to conclude much other than the observation that the B3121 might be sitting on a gray line when used in the E9X M3. I might still give mine a try, but if I do, I will be carrying a battery charger around with me before I am convinced that it is working for me...
Yes, definitely gray areas here - including cars that "drain" differently when off. I would not bother at all with a battery charger though, I've never had problems starting whatsoever, just the small electronic glitches I've mentioned.