Replace BMW Key Battery It's probably time to change your battery if your BMW key won't allow you to open your car or turn on the engine. Fortunately, it's an easy fix. You simply need to remove the key fob, then replace the battery, and then gently put it back. https://thekeylab-co-uk50268.blog5star.com/30558543/5-killer-quora-answers-on-bmw-3-series-key-fob