Replace BMW Key Battery It could be time to change your battery if your BMW key won't allow you to open your car or turn off the engine. It's a simple fix. You simply need to remove the key fob, then replace the battery, and then gently put it back. https://car-key-repair50935.blogcudinti.com/30142559/the-ultimate-guide-to-bmw-3-series-key-fob