Replace BMW Key Battery It's probably time to change your battery if your BMW key won't open your car or turn the engine. It's a simple fix. All you have to do is take off the key fob cover take it off, then replace the battery, and insert it gently. https://the-key-lab92271.luwebs.com/30760368/20-fun-informational-facts-about-bmw-3-series-key-fob