Just spend the $180 or so to buy a proper aftermarket battery. It's really not that bad for every 4-5 years or so...
No initialization is required via GT1 computer. Just plug & play. The problem with the Mini Cooper battery from what I remember (when I was doing research on what battery to get) is that it has less cranking amps and other specs inferior in comparison to OEM.
Here, I dug it up for you. This is what you can buy from your local auto parts store:
http://www.zpost.com/forums/showpost...6&postcount=47