Replace BMW Key Battery It might be the time to change your battery in the event that your BMW key won't open your car or turn off the engine. It's an easy fix. You simply need to remove the key fob, then replace the battery and gently put it back. https://car-key-reprogramming49217.nizarblog.com/30205156/what-bmw-key-fobs-experts-want-you-to-know