That's because BMW ECUs adapt to the lower voltage as the battery ages and instruct the alternator/charger to provide more current. Replace the battery and the

That's because BMW ECUs adapt to the lower voltage as the battery ages and instruct the alternator/charger to provide more current. Replace the battery and the ECU would cause it to be overcharged unless you notify it of the replacement. Yes it's an over-engineered system, but ... German car.