Replace BMW Key Battery If your BMW key isn't opening the doors of your car or turning over the engine, it could be time to change your battery. Fortunately, 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-repairs07930.bcbloggers.com/29633714/20-resources-that-will-make-you-better-at-bmw-3-series-key-fob