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. You simply need to remove the key fob, then replace the battery and gently place it back. https://thekeylab05326.bloggazzo.com/29558140/3-reasons-you-re-bmw-3-series-key-fob-is-broken-and-how-to-repair-it