Have a '12 997S Cab that i drive fairly regularly. Didn't drive for a few days and last night battery was dead. Checked and no inside lights or anything was left on. I bought the car over the winter and had it on a trickle/battery tender until April, so it was fully charged then.

I have a battery/alternator/starter-motor tester that when the car wouldn't start said "weak" which according to the instructions means "ok" but needs to be charged. After a jump start the load test (picture shown) says battery is good. I trickle charged the battery overnight and it still didn't finish charging so it was pretty run down. Tested the charging system (alternator) and put it through it's paces, AC on, heated seats, lights, ventilated seats, put the top up/down a few times, and can't get any tests to fail. So the question is why the heck did the battery die? I'm more concerned about a problem with the electrical system in the car. Shouldn't be going dead, especially in warm weather. Any known issues to ask the dealer about?

 

Hmm good question. Since you already tested the battery and the alternator and didn't get any fails, since you have a '12, I would take it to the dealer and make them work it up - get your dollar's worth out of your warranty!

 

Ok, so I just spoke with my service advisor at my dealer. I told him everything is checking out, alternator to battery, and he says if you leave the car unlocked like I did for several days these Porsches' electronics will drain the battery. He says to lock the car whenever im going to leave it for longer than a day to avoid battery drain as it shuts off power draining modules when locked. I've never had this happen with any other make of car but he claims it's a Porsche 'issue'. Can anyone comment on that?

 

personally, id go to walmart, get the $128 H7 battery and be done with it.

 

Is that a better unit than the Audi/VW ones the dealers replace with?

 

Cant beat walmart had mine for 2years plus if it goes bad u can return it within a year though

 

Have the battery load tested at Autozone or similar parts place. My money says they come back with weak or dead cell. Trickle charger won'tcharge a weak battery. Porsche can check it as well but Autozone will do it for free. Then go buy a new battery. As for the " Porsche's just do this to batteries.. " myth, that's dealer BS. Alarm system isn't pulling enough amps to drain a battery the size of the one in a 911 in a couple of days. If battery is good, check the charging circuit for voltage drop between alternator and battery.

 

Here's the load test results, no problems. Also getting 14v off alternator so charging is good too. Can't find any obvious problem.

 

I have heard of the electronics draining issue. Also even in locked position it does drain some (much less than when open)
Actually if you lock your car and do not drive it for more than a week then the keyfob remote does not work and you have to unlock it with the key. (read the manual states it there)
This is done due to prevent drainage if one is storing it long term

 

Pic seems to be showing 11.5 volts but regardless, static reading from the battery positive terminal should be 12.6 V. Same reading with engine running should be 13.5 v or better. Durametric should read 13.8 v at terminal 30 with the engine running. If you're getting 14v at the alternator b+ that's great.

 

Well that's under load (button held) for 10 secs. It's in the range for the amp battery rating. Battery is good. Here's some more I found out:
http://forums.rennlist.com/rennforum...94-post17.html

 

Sounds like you've exhausted all your diagnostics. May be time to just replace the battery. Porsche batteries act much differently than any others I've had. I've had a year old battery fail to crank the car, charged overnight and started fine the next morning only to be dead that afternoon. Replaced the battery and have had no problems since.

 

The mystery is still alive as the OP is still hashing this issue out on Rennlist now. Real mystery is why the OP refuses to take the battery to shop that can test it properly.

 

Ummm, I appreciate your past post, but as I said (and showed) I am using the same battery load tester you find in the repair garages. The car is fine at this point, the battery, alternator and starter motor all test fine. So, no real mystery, just going to keep an eye on it for a while.

 

Did you leave the key in the ignition? Even in the "off" position, that REALLY drains the batteries on 911s.