Battery dead -- cause of drain?
 

After driving my '04 Thursday extensively, now on Saturday, it won't start. Battery completely dead. Had to connect jumper battery to open hood, and then jumper cable to discharged battery. Radio, lights, etc. functioned, engine would make one (feeble) attempt and turning over, then clicking noise. Turned key back to off position, and I hear this soft, two part "thunking" noise about every 15-20 seconds. I repeated this cycle three times. The thunking continued each time until I gave up and disconnected the jumper cables. The battery is now back to totally discharged. No more thunking noise.

Any ideas what I should do next; or what the thunking (or clicking) noise was? Thanks in advance. Hurts to have a dead sleigh on Christmas eve. FYI, it is a one year old factory battery.

Barring any suggestions, looks like the car is being towed to the dealer.

Before towing the car away I would take the battery out and have it tested. If it has a bad cell it will not even take a jump start

Good luck

If you are positive your battery (I would take it out and have it tested - even new batteries can have a cell go bad) is good then you need to put an amp meter inline with the battery. Then remove fuses one at a time until you find the fuse circuit that is drawing all of the power. Normally a 996 draws about 40-60ma (as I recall).
Once you find the circuit where the drain is then it should be fairly easy to trace down the component.

I just had to replace a 3 month old Interstate battery that wouldnt hold a charge. It happens.

Just returned from the Zone...
 

...AutoZone says battery is fine. Problem is likely related to that thumping noise I referred to in original post. My wife said she heard it in the garage last night but thought it was a tree limb blowing against the garage. No clue what would be making a thumping sound every 15-20 seconds....it almost sounded mechanical.

Do I have suggestions? Uh, yeah - a few. I had a 2 year old OEM battery go bad on me 2 weeks ago. See my lengthy thread on this. Trickle charging didn't help, and it barely was able to be jump started due to a bad cell. It turns out, one of the cells was sulphated and acid leaked through the vent tube to the underside of the car - fortunately, the battery case was intact. Because I drive so little, the battery wasn't covered under warrantee - I wouldn't have replaced it with a Porsche battery, but I wanted my dealer to ensure there wasn't any damage - there wasn't. Difference was that you were acturally driving your car. Which I don't do enough of. Apparently, battery cell damage is not uncommon to OEM batteries.

BTW, did you find out what the thumping in your garage was? Poltergeist perhaps? I can't figure out from your post if your battery is still dead or has been resurrected!

Still Comatose...
 

...awaiting a flat bed for a trip to the dealer Monday morning. No ghosts in the garage, just a 911 that refuses to start. No amp meter, so they'll have to figure out what or where the drain is. Thanks, everybody.

Keep us posted as to what the cause was.

Years ago on my 993, just as I was about to leave on a 2 week trip, one of the fans kicked on by itself even though the car was turned off. Although the fan running after turn off was not that unusual, it never turned off. It just going and going. I had to disconnect the batttery to keep it from draining while I was gone.

It sounds like you might have some relay that is staying open and not turning off which drains the battery. But then I can't think of anything on a 996 that might make a thumping sound.

Fixed, thanks to AAA.

Kid had adjusted passenger seat, and the power seat control had become lodged in the "furthest back" position.

Seat control repeatedly attempted to move seat;
caused thunking noise, and drained battery.

After jump start, and releasing seat control from stuck position, I'm good to go. Thanks!

Now, THAT'S weird, but it explains everything that happened to your car. Glad it's fixed.