You don't HAVE to use BMW coolant. It is not magical coolant. The most important part is to make sure you follow the venting procedure, which is a simple process. Do a search on here. I believe eninty has a DIY on here. How I do it is to remove the undercover, remove one of the blue screws to the radiator, refill, vent, refill, and vent (not a typo; when you vent you will need to add more coolant. Eninty has you remove the waterpump hose(s) which can be a PITA. It is the correct thing to do, but I skip that.
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) go here http://www.e90post.com/forums/showthread.php?t=727091