996 Battery drain

Hi, I'm new to this group so please go gently. I've tried to read everything I can about the battery going flat on a 996 but I've never found a conclusive answer. My 2000 Coupe lasts about 2 to 3 weeks on a new battery before it's dead. It's outside so I can't trickle charge but did have some success with a solar panel in the summer. Is there a known cure or just poor design. Thanks,

You may half a short somewhere draining the battery but this can easily be identified by measuring the battery whilst removing fuses. You have the immobiliser and alarm on all the time when not in use which doesn't help. If it's locked in a garage at home you can leave it unlocked and see if that helps. Also, the system goes into hibernation mode after a week or so to save power - it's not that what you've experienced is it, or is it deffo flat battery? Mine only lasts about a week or so now but my battery is about 8 years old. Use mine daily though so never an issue for me. Edit: sorry, just read its outside.

2-3 weeks to go flat would be a small discharge but that depends on if you mean flat as in the dash lights come on but it either doesn't want to spin over or does so slowly .. or if you mean its flat as in its totally dead with no dash light .. no nothing ! That would be a larger drain . In essence with a good battery and an alternator that was charging correctly then about 5-6 weeks of not using the car would cause a battery that would not spin the starter fast enough to start it . usual items .. a tracker has been fitted and the battery on that is now dead .. a pulsed approx 0.8 amp discharge on an amp meter every 30 - 60 seconds . The radio whether porsche or aftermarket is another common area ... finally the glove box light , the switch breaks and the light will be on all the time .. stick your phone in it on record and close the box .. remove and check the video to see it goes out . I'm more than happy to explain in detail how you use an amp meter and how to check the charge rate to find battery issues .. for a battery check though you need a dedicated tester to check it .. As it will take me a good 20- 30 mins to write this out then i do need you to say you have a voltmeter and want to do it yourself .. in which case i would be more than happy to spend the time assisting you . If you are more inclined to just take it to a garage then i'd rather not spend so much time .. no offence .

What do you think of fitting an electrical cut-off/disconnecting the battery Iain?

Hi, thanks for the replies. When the battery is flat it's either unable to spin the starter or the dash light all go off as I try. Sometimes if I leave it too long the alarm goes off and can't be stopped. The alarm does go to sleep after a week and I unlock and lock with the key, switch off the alarm with the remote to get in. I have a CR22 radio and CD changer fitted. I don't have a glovebox as such, just the lockable centre console, I'll check if there's a light in there. The front boot light doesn't come on when I open it but I'll try the phone trick to see if it comes on when shut, that's a long shot. I'm happy to follow instructions regarding testing with a volt meter, I've just rewired a Triumph TR4a so getting used to electrical issues although that's 40 years older and much more simple. Thanks in advance, Mark

I mentioned this in another thread recently as I had a major battery drain problem when I bought my 996 C2 after being in storage for 4 years...the ignition barrel was 'live' the whole time thus draining the battery in 3 to 4 days. It took a new battery and alternator to find out issue but Tower Porsche located the issue and fixed it sharpish... Get your technician to check the ignition barrel...

The Y section of the main power cable/harness may be another candidate: http://911uk.com/viewtopic.php?t=138333&highlight=cable

You can fit them on upto and including a 993 but from 996 you then have issues .. These are normally fitted close to the battery .. so the bonnet / frunk area .. you would need to lock the car , isolate then close the bonnet .. but then you can't open the bonnet .. the manual release has a lock solenoid .. electric switches and forget it .. jump pack on the fuse box tab to get the bonnet open . You could disconnect the manual release type system solenoid so that it never locked .. you would then open the car with the key .. pop the bonnet and switch the isolator .. at that point the alarm would trigger .. you need the keys in the ignition and in the on position . You will also get flat battery symptoms .. you need to reset the windows .. radio code .. steering angle sensor so a drive over 6 mph to get the light off .. throttle adaption . Over all it's just not feasible on these cars ... well it is but too many issues to make it viable i feel . For security then fit an immobiliser .. for long term storage then disconnect the battery or a trickle charger . OP .. PM me if you want a write up of basic checking for battery discharge checks .. i have time over the weekend to do this if required .

I have bought a little battery monitor on Ebay (£20)and I have a app on my phone that tells me the stat of the battery. I can also test the performance of the alternator and how the power starter motor is drawing. It also tells me the history of the current draw on the battery.

Have you checked what the current draw is of the battery when it's being left? That will give you an understanding of the problem. You'll need a multimeter and a spare half hour but it's a good check to do if you're concerned. I don't know how handy the OP is with this but here is a good guide: https://www.wikihow.com/Find-a-Parasitic-Battery-Drain you will want to leave the car for a while so it properly goes to sleep - ie powers down all the systems.

One of the reasons I like my 996 is that it is like being on the TVR forums a few years back. Battery drain was a popular subject... I have had this a couple of times and one was a faulty new battery and another a fading alternator (Porsche) It took me a while to crack that one but do make sure you sort it. A simple volt meter is cheap and useful and I worked out the fading alternator with a cigarette lighter volt meter on the Boxster but the 911 has a volt meter so watch what goes on under load. If you are still not happy, a product called battery brain was a popular choice with the owners of Blackpool's finest. You put it in line and either switch it of remotely and I think there is an option that it senses the power situation and cuts the circuit if it gets to low. Getting the battery load tested and checking the drain would be my approach.

When I first purchased my 911 I was annoyed on day 2 when the battery was flat; should have know that was why car came with a battery charger... Anyway, my issue turned out to be the Y cable between alternator / battery / starter and a simple fix. Symptoms were dash voltmeter showed lower output once car was warmed up as resistance on that cable increased. While I was in fixing the y cable I also swapped out the regulator on the alternator for a bosch p/n off amazon and I uograded the battery in size by 1 increment (seems the battery tray can take 3 different sizes) for a Bosch S5 010 85Ah. I did also swap out the starter at same time but this was due to it screeching on use down to a dry bearing. Since I did all this more than 18 months ago, charge situation is great 14v or just a bit under with full load.