Thanks for the info. I ended up getting the diehard battery (size 49), from Sears, and almost everything works (side mirror keeps moving around for no apparent reason; but I've heard that the X3s tend to act a little funny for a few days after replacing the battery, so I'm keeping my fingers crossed).

As for the heater, I live in Texas, so I'm guessing I won't need that. I did order a smart charger from Amazon, and will try that when not using the vehicle. The reviews online claim it can double the life of your battery, but the proof of the pudding is in the eating.