Battery registration and BMS resets: the step German cars punish you for skipping
Most European cars built after roughly 2008, and a growing number of Japanese, Korean and American models, run a battery management system that tracks the battery's age, capacity and charge acceptance. The alternator's charging strategy is tailored to that data: an old, tired battery gets charged harder and more often. Fit a new battery without telling the car, and the BMS keeps applying the old battery's aggressive charging profile to the new one. The result is chronic overcharging, gassing, shortened life, and on many cars a stop-start system that refuses to operate.
The fix is battery registration (BMW calls it registration, VW-Audi coding, Mercedes a BMS reset), performed through the OBD port with a diagnostic tool in five to ten minutes. If the new battery differs in capacity or chemistry from the old one, the tool also updates those parameters. This is a legitimate line item, and a mobile technician quoting for a German car should state plainly whether it is included. A quote that is silent on registration for a car that needs it is either incomplete or the technician does not carry the tool.