Intermittent Dead Battery
 

2002 x5 4.4 Battery goes dead overnight. then is good for a month..then dead again..Battery tests good..no draw.. Doesn't necessarily have to be a cold night to go dead. Last night it was -12, car started right up. I'm thinking the heater control thing with the fins on it.? I get heat top and bottom and cold in the center vent. Even with the dial turned to red. Would that draw the battery dead intermittently?:dunno:

How old is the battery? Even if it passes a load test, it may be failing with age.

The heater fan control is called the final stage resistor. Yes, they can go bad, and be the cause of a parasitic current draw that prevents the vehicle from going to sleep (thus flattening a battery overnight) but don't replace anything until you diagnose it, throwing parts at a problem is always more expensive than figuring out what the actual problem is first.

You need to do a parasitic draw test. Instructions are posted here.

Whether you get heat or not out of the center stack vents, that doesn't flatten a battery.

Instructions are posted where?

Check post #41, & #42 in this link:
http://www.xoutpost.com/bmw-sav-foru...es-fast-5.html