I previously complained about my E83 eating batteries. I am taking it in to another BMW shop next week. It will be interesting. I bought a cutout switch and put it on the negative terminal of the battery. I found it cheap on Ebay but it does not fit really well. Both terminals are too big.
I found out something interesting though. Many of the auto stores will sell you a 48 battery. The 49 battery fits like the stock battery, has a lot more cranking amps, and is the same price. I bought the Bosch from Pep Boys for $110 with a 3 year full refund and 96 month pro-rated.
I am cussing BMW engineers daily for designing a car that eats batteries. $(*#&(@(@&!!!!!!!