Five month old battery died yesterday. Had AAA test it, and they found the battery was draining even with everything shut off.
E39s seem to have the same common problems. So far, I've had a non-opening trunk, inconsistent A/C fan speed, and a broken CD changer - all of which are potential battery drainers.
I've fixed the trunk problem (broken wires leading into trunklid), and the CD changer hasn't worked the past 4 years or so, so I'm guessing it's the FSU. Guess I'll bring the car to the indy mechanic tomorrow again....