Battery Keeps Running Down

Hi, We recently bought a 2004 996 C2 Targa. It seems to be in very good shape, and drives very well. Soon after we bought it, the battery died, completely. Since it wasn't the right battery anyway, and I had no idea how old the battery was, I put a new, correct, battery in. Despite this, if we don't drive the car for a week (or less), it won't start. There's no light left on inside the car; in a week, the battery's not completely discharged, just doesn't have enough ooph to start the car. The car is garaged. Now, I've owned many cars over the years. We own four other vehicles. Every car I've ever owned (well, except possibly the Fiats) would start without a complaint even if left unused for weeks. Not this one. I've done some research, and this seems to be a not unusual complaint. Is this just the way it is? If so, why? If not, do I need to look for some sort of slow drain (while ignoring all the complaints about 996 Porsches that don't start when left for a few days)? Thanks. Mark

I think there's a parasitic drain somewhere in the car. This isn't normal. Here's my story: When I got the car, the service records indicated that it had had seven batteries under warranty. I put in a fresh one, and soon after it started doing what you describe. People told me it was just because I wasn't driving it enough. Eventually, I spent the money to trace the problem and, lo, it turned out the car had two Lojack-type devices installed in it, each one by a different owner (and by the dealer!). I had those taken out and a new battery put in, and in all the years since then I've been able to leave it for days or even weeks and still get a good, strong start when I turn the key. Trace the issue. It will drive you crazy.

That makes sense to me; it's hard to believe such an expensive, fine car could have been designed to drain the battery in a few days. I'm told that there's a common problem with the ignition switch, which can result in things not shutting down completely, with this result. I'll spend some time with a voltmeter, and report back in a few days. Thanks!

GL tracking your battery drain. As mentioned by BruceP, it shouldn't been depleting your battery and your voltmeter should help you find your problem.

Always lock the car as a locked car takes less battery. Not that I am saying leaving the car unlocked is draining the battery. Far from it. Hope you solve your problem.

a good shop or maybe even an auto parts house can put a tester on your battery and see if it has a draw on it while everything is "off" it will at least let you know that you are looking for a drain as opposed to a charging issue OK enough help - time to post pics newb !! no free lunch around here - tell us about yourself and your car - well...actually just your car WELCOME

I had a similar issue a few months back, but it got to the point where the battery would go flat over night. short version; new battery installed, charging correctly, so started pulling fuses to narrow down the drain. Main panel no drain, pax side no drain, narrowed down to starter, alternator or wiring harness battery to engine compartment. On a whim, figured I try a different approach, if I'm loosing power, I must be gaining something else, heat. So out comes the IR thermometer and presto, the alternator is 20deg warmer than its surroundings!! One alternator later, the car can sit for weeks at a time(unlocked) and start fine.

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What a creative way to track down the culprit!

do a proper battery drain test and alternator charging test. both can be done easily with a multimeter. youtube car battery drain and alternator battery test. you'll see how it's done. if both test fine, it's your battery. you can also swap the battery and do it trial by error.

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Why? I would think that the locked car is monitoring for interior movement for the car alarm, and an unlocked car is not doing this. Please edumacate me.

In the 996 when you take your key out of the ignition certain systems are turned off. When you lock your car even more systems are shut down which causes less battery drain. It does make a difference. So its best to never let the key in and always lock the car for less battery drain. After locking the car in about 5 days IIRC, even more systems will be shut down including the ability to use your key fob to unlock the door. When this happens just put the key in the door and unlock it manually. Then make sure you put the key in the ignition and start the car or at least turn the key to the first position within about a minute or the alarm will go off.

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OK Steve read all the postings in the 2 pages of the link about sleep mode which will fully explain the reason why. Porsche87 has it correct. http://www.6speedonline.com/forums/9...o-quickly.html

Hi Folks Battery totally dead after 48 hours. I now know how to get into the luggage area and at what voltage the alarm goes ballistic in the middle of the night. New battery and alternator as the output was a tad low and we suspected the back leakage too. Good job as the pully clutch was siezed anyway. We next plan to go through the the fuse/relay pulling exercise to track it down but wondered if 124Spider found his fault? What was the "ingnition switch fault" or how was it diagnosed? When we fitted the alternator I checked the drain and it seemed to drop with the car UNLOCKED. But I didn't do a long term test. I just thought we had cured it. 😳 Has there been a history of alarm problems pulling juice? It's a UK car. I notice the spoiler deployed at least once when it went flat. Is this the engine temp monitor activating cooling when stood? I would be grateful for any clues and pointers, it would be interesting to see if there is a statistical trend. Ta Garry

FWIW, my '03 911 Cab will always start - even after a week of sitting in the relatively warm garage. However, if I hook up the battery tender, it typically takes 4-5 hours (at micro amperage) to full re-charge it. Now the battery is a relatively new (1 year or so) one - and I was told it was "one size below what is proper for this car" (it's, I think, a group 7 unit). As the car never gets very cold (typical garage temperature is at least 55 degrees F), and if I drive somewhere the car is re-started at maximum a few hours after shut down, I'm not worried about it (and I have a AAA card). This car has a lot of electronic nannies so a relatively "good" battery might run down in two weeks or so. I think I'll purchase a proper sized unit after this winter.

Just a thought on this. Glovebox frunk and engine bay all have lights. Put your phone inside each recording a video and see if the lights are turning off. Could be a micro switch not shutting down the lights. I've left mine over 2 weeks and no problem starting.

Well I think we have.... Traced a 1.7 amp drain going to the PCM2 unit in the dash.... Radio/Sat.Nav./Phone module. The sat nav was coming back with a "fail to start" error on turn on so that may indicate continued "boot" keeping the Bus from shutting down? Any thoughts? I know the previous owner had an issue with the battery in as much as it had probably been flat anyway as the earth strap was loose. Have already fitted a new one and alternator. Since the start of this the SIM card draw catch has gone too. I know the parts for that are about �20 but still need to track down the popped components that were leaking power and it will need better power surge protection. I think a boost charge may have blown it? Now looking at UK options to fix it. Found a couple but still debating whether to replace with 2015 technology rather than spend vast sums just for originality? Will it have a security code too? Not got that far though the manual. If I buy a second hand working unit will it need coding to the car? Love the idea for recording the box lights with a mobile! So good I wish I had thought of it? Onward.....