MB 911

I have a 90 964 C2 and about every 3 months I have to replace the batery. It has a 36 month warranty so the swap is free but its a PIA. I can't find an abnormal drain and I have removed each fuse and replaced and still no clue.

Any suggestions?

demonfish

if anything its an OVERcharge??

right size fan pulleys?

ok voltage output?

maybe the regulator letting to much out...

sleder

Sometime the interior light button on the drivers door sticks and casues a constant drain. Check that. A kill switch will eliminate the PITA when not in use shut the battery off and turn it n when you want to use the car.

SKM

I've seen faulty heater & AC control unit cause battery drain/failures.

demonfish

is it a drain or a failure????

jjbunn

I have similar problems. I've eliminated most of the usual suspects. My current best theory is that it's a sticky solenoid in the driver's side door locking system, which would explain problems I'm having there as well.

To keep the battery fresh, I bought a Porsche battery trickle charger that I simply plug in to the cigarette socket every time I park the car in the garage.

SKM

The heater and AC control unit worked, however it was constantly was drawing power and drained the battery.

Frank 993 C4S

Cheap solution - doesn't fix the problem but prevents the battery from discharging. The only negative is that you need to reset the clock:

J-F-O

I had a similar probem

Turns out the issue was with the radio. The lights in the face plate never went off therefore draining the battery over time.