Replace BMW Key Battery It could be time to replace your battery if your BMW key won't allow you to open your car or turn off the engine. It's a simple fix. It's as easy as removing the key fob, then replace the battery, and then gently put it back. https://car-key-reprogramming49217.nizarblog.com/30317310/how-to-tell-if-you-re-ready-to-bmw-key-fobs