Z3 Phantom Battery Drain

My car has decided it is no longer going to hold a charge over night.

Things I have checked:
Battery - it has been tested, but I suspect water in the casing + freezing temperatures
CEL's - All have been delt with - P0505 and P0455
Sound system - The entire system is ran through a bank and isolator switch

Any ideas past that that could be the culprit?

Check if the wiring loom near your driver's side trunk hinge has frayed wires causing a short, or if you just haven't shut your trunk completely causing the trunk light to stay on continuously.

Start with http://www.bimmerfest.com/forums/sho...=battery+drain

Searching on "battery drain" will turn up a ton of info.