Mine is the damn tcu again. The one that was in my X5 was bad completely and when reconnected killed the battery.

The new one worked fine for a few weeks and now its killing the battery but at least it still works.

I am SO replacing the entire stereo system in my X5 at the end of the month.

This will eliminate the tcu, nav disc unit, cd changer and the nav head unit with a radio that will completely turn off when I cut the car off.

I dreaded losing the ability to reset the mpg and such but its worth it for peace of mind not having to worry about a dead battery.

My tcu is waking up and draining the battery and sometimes it doesn't shut down at all to start with. Took awhile to verify it but that's what mine is doing.