Wow, thx!!! Mine is original, top of negative post was stamped with "23 05". That means my battery was manufactured the 23rd week of 2005. Thanks again.
If no codes are being thrown use Chevron Techron fuel injector cleaner (concentrate). It solves rpm fluctuating upon cold start-up. Also, for most BMW problems start off by scanning your car with the Peake Research Tool. It contains the actual BMW codes. If you want to register a newly installed battery for free (just buy a $10 cable) and google/download BMWLogger