A dead battery in BMW is absolutely vexatious. However, a battery draining is something that can be avoided. But for that, it is important to understand the cause. This slide contains 4 key determinants due to which the battery of a BMW keeps draining. Besides knowing the causes, the BMW parent should have to inspect the battery regularly, do a terminal test periodically, keep the battery terminals clean, check the charging system and perform alternator diode test from time to time- to avoid sudden battery failure in the middle of nowhere.