Battery discharges overnight

[cmarktaylor]

Greetings fellow Porschephiles, I searched the forum hoping to find an answer to my current issue with my 2000 996 C2 with 123,201 miles. It has killed 4 batteries since Dec. 2017 and I need to find the cause before I take the last battery back for a warranty replacement. I'm five weeks out from back surgery and won't be released to lift anything heavier than a gallon of milk until after Sept. 18. but I'd like to solve the problem before then if possible. Has any one had this issue and solved it, if so I'd love to hear the fix, and any and all input is welcome.

[JFP in PA]

You need to test your electrical system for parasitic draws; requires putting a digital multi meter between the + post on the battery and the cable, letting the normal draw fall off (1 hr.) if you see more than 40-60 milliamp's, you have a drain. Then you pull one fuse at a time until it drops into range. Last fuse pulled is the circuit with the drain on it.

Good luck.

[cdrik915]

First , do you remove the key when you stop and park your car ???

[cmarktaylor]

Thanks for your input. To answer your question, I do remove the key and lock the car when its parked in public, and remove the key but don't always lock it in my garages. I've pulled each and every fuse one at a time and none of them had and excessive amp draw. I was talking to a fellow auto enthusiast who's into British cars and he suggested disconnecting the alternator. He commented that its possible for one of the diodes to cause the battery to discharge. I've put a cutoff switch at the battery to keep it from discharging while the car is parked for any period of time between drives.

Again thanks for your input

[BYprodriver]

You need to lock the 996 so that it goes into "sleep" mode to minimize drain on the battery

[RarlyL8]

^^^
What he said. These cars have a crazy amount of electronics that remain on even when the engine is off. To turn everything off you have to click the fob and lock it. Stupid yes but they all do that from 993 on up.

[brownspeed]

I had a similar problem on my 997. on 997 the horn sounds if something is amiss e.g. frunk being open. (which I was convinced was the issue- frunk light being on & horn was sounding when locking)
it wasn't.
after a forensic review of all lighting circuits I found the glove box light was permanently on due to a large button being lodged down the back of it- holding off the microswitch. this killed my battery.
hope it's of help

[cmarktaylor]

Turns out my problem was a bad diode in the alternator. Thanks for your help and input.

[neadaporsh]

Same car.............same problem.........my tech replaced the "Y" cable and problem solved.....it ties everal functions together and has a tendency to short out or corroded terminals are also a problem