Why does my battery keep dying and won't keep charge?

Greetings, Unless your battery is just dead...you most likely have some kind of power drain. On the E39 chassis a common source of battery drain is the final stage resistor....A final stage resistor can fail in many different ways...typical signs of failure are: Fan (for the a/c and heat) running constantly even with the ignition switch/key turned off (this will drain the battery if the fan runs all night), or the fan being very erratic and not moving at the same speed that you have it set for, to it having a complete mind of it's own and just coming on off randomly at different speeds. I hope this helps, Kind regards, Stephane Grabina BMW Excluservice Rockville, MD 20852 www.bmwexcluservice.com

Don't know

Could be your battary has no water or you need new battary posts