[tm30]

Maybe this is a stupid question, but what does this do to your warranty? One could argue you're making a significant structural change to the car by permananently eliminating 70lbs and certainly altering the weight distribution that these cars are designed around. Weight distribution was important enough for BMW to locate the battery underneath the trunk compartment, I would be concerned that they'll look at this and say, "you have an entirely different car than what BMW built for you, therefore, the warranty is void."