Originally Posted by The1
Honestly, I'd recommend getting a trickle charger, or install a battery switch.
also, depending what year your car is, make sure you have a way in and out of the trunk when you disconnect the battery, they took out the trunk key on some of the more recent models and people have locked themselves out completely.
even with the stock battery, the BMWs have so many electronic systems that the battery really doesn't last long.
I've got an 08, so i have a key to the trunk