Battery draining quickly - question on Porsche dealer's proposal

[TimeTraveler]

6 weeks ago I bought a Porsche 911 Carrera 4S Cabrio 997 from 2006.

The battery has drained already four times, after standing still for or 7 days or 5 days or 3 days, with as consequence that the car could not be started anymore.

After the battery got empty and I got it jumpstarted, it charges fine.

After short trips and a break of for example 3 hours the battery is fine.

On a 400 km trip the battery was fine as well.

The battery was tested as part of the 111 points check by Porsche, and was fine at purchase 6 weeks ago. Also the road assistance did test the battery twice and said it was fine, and charging as well.

It looks like there is consumption of power when the car is turned off. I was suspecting as a possible source for the problem the integrated audio system as when the car is turned off I still hear the CD player searching for a CD. I already used an audio cleaning CD, but this searching of the CD is still there when the power is off.

I took the car to the official Porsche dealer to get it checked.

Now they say the alternator needs to be replaced because it only gives 12.5 Volt, and it should give 14 Volt.

Given the pattern where I get the problem this does not seem the right conclusion.

When I get a new alternator I'm afraid there would still be a drainage when the car is standing still for a couple of days.

What do you advice ?

[Mijostyn]

Hey Time traveler,

Pull the fuse on the PCM module and see if this stops the problem. If it does your PCM is neurotic and needs to be replaced. Go aftermarket. Alpine and Kenwood are nice.

Next, check the battery's build date. It is stamped on one of the terminals. You may need a magnifier to read it. If the battery is over 6 years old replace it. Even if it tests OK it may be bad and it will fail soon anyway as the average life span is 6 years. Best not to get caught with your pants down.

I'm not sure about the alternator, maybe JFP would like to chime in on this??

Edited April 4, 2014 by Mijostyn

[JFP in PA]

6 weeks ago I bought a Porsche 911 Carrera 4S Cabrio 997 from 2006.

The battery has drained already four times, after standing still for or 7 days or 5 days or 3 days, with as consequence that the car could not be started anymore.

After the battery got empty and I got it jumpstarted, it charges fine.

After short trips and a break of for example 3 hours the battery is fine.

On a 400 km trip the battery was fine as well.

The battery was tested as part of the 111 points check by Porsche, and was fine at purchase 6 weeks ago. Also the road assistance did test the battery twice and said it was fine, and charging as well.

It looks like there is consumption of power when the car is turned off. I was suspecting as a possible source for the problem the integrated audio system as when the car is turned off I still hear the CD player searching for a CD. I already used an audio cleaning CD, but this searching of the CD is still there when the power is off.

I took the car to the official Porsche dealer to get it checked.

Now they say the alternator needs to be replaced because it only gives 12.5 Volt, and it should give 14 Volt.

Given the pattern where I get the problem this does not seem the right conclusion.

When I get a new alternator I'm afraid there would still be a drainage when the car is standing still for a couple of days.

What do you advice ?

If the alternator is only putting out 12.5V, it is definitely bad as you should be around 13.5 to 14.5V. I would also have them check the battery and starter cables which are notoriously problematic on these cars. Porsche has released updated cables to address the problem.

[TimeTraveler]

Thanks for your feedback.

The Porsche dealer has replaced the alternator. They showed me the test results afterwards: the old alternator was putting out 13.4 V without any consumption load switched on. The new alternator puts out 13.6 V with the full load switched on.

They also changed the battery, not because of the fact the battery condition was not good anymore but because of the fact the physical size of the battery was too big. Strange that no comment came out of the 111 points official Porsche check when I had it checked before purchase in the city where I bought the car, as I also explicitly discussed the condition of the battery at the Porsche dealer where I had the 111 points check done.

When I now asked for which car this battery is meant to be used, they told me it's for a bus...

I'm now just back from a 10 days business trip, and checked if the car was starting after standing still for 10 days, and it was, so I hope this is an indication that the problem is fully solved.