http://www.bimmerfest.com/forums/sho...hlight=battery
Do a search = battery (here and on the other boards)
a lot of threads will come up.
Also this thread and the searches belong on the main board or maintenance sub boards . Unless you have a huge aftermarket stereo installed.
A good independent can change and register the battery or you can do it yourself and register it with a coding kit, Bav tool or take it to an independent . You just need to match the size and capacity . I used and Interstate mtp94r /h8 for a 90ah battery myself.
See Diy and maintenance sub boards and coding board for procedures.