Replace BMW Key Battery If your BMW key isn't opening the doors of your car or turning on the engine, it may be the time to replace your battery. It's a simple fix. It's as easy as removing the key fob, replace the battery, and then gently put it back. https://car-key-replacements78786.blogs100.com/30620178/10-things-everyone-hates-about-bmw-3-series-key-fob