You have posted in the E90 forum.
You can replace the battery with any brand you like, as long as it's compatible - especially with the requirement of the vent tube.
You then need to register it. That can be done at any place that services BMWs: dealer or independent. Dealer might charge an hour labor. This "registration" process is used so that the Intelligent Battery Controller will know how to condition and charge your battery to extend it's life as much as possible.