Battery dead

[etienne]

Hi Guys

I own a 2006 997 C4S which I bought 10 months ago. The car has now done 30 000km's. I have noticed a progressive slow cranking over the last few weeks. I use the car on a daily basis for short journeys. When I had it serviced recently I asked the dealer (350 km away) to check the battery due to the slow cranking. They reported that the battery was fine. On Friday the car would not start at all. I removed the battery and had it tested at a battery shop where they said it was fine, just completely drained. What do I do now??

I had the same problem with my previous car, a 996, last year, when I gambled and tried to drive to the agent. I made it half way before the car stopped in pouring rain with the battery dead in a remote area. Not something I would like to do again...

I would really appreciate any suggestions.

Etienne

South Africa

[JFP in PA]

If the battery is draining but otherwise good, and there are no undo parasitic drains on the system, you probably have a problematic alternator. Check for electrical drains by putting a digital voltmeter set to current (mA) between the positive battery cable and the positive battery terminal. You should see something around 60 mA or less (normal current draw). If it is higher, something is pulling current out while the car is parked. You can locate the circuit by pulling the fuses one at a time until you see the draw drop into its nominal value; the fuse you just pulled is the problem circuit.

As for the alternator, you can use the same meter to check the voltage output at idle, should be 14.3V or so. If it is below 14V, you probably need a new voltage regulator for the alternator (same regulator is used in Audi, Mercedes, and VW cars, so you should be able to locate one).

[etienne]

If the battery is draining but otherwise good, and there are no undo parasitic drains on the system, you probably have a problematic alternator. Check for electrical drains by putting a digital voltmeter set to current (mA) between the positive battery cable and the positive battery terminal. You should see something around 60 mA or less (normal current draw). If it is higher, something is pulling current out while the car is parked. You can locate the circuit by pulling the fuses one at a time until you see the draw drop into its nominal value; the fuse you just pulled is the problem circuit.

As for the alternator, you can use the same meter to check the voltage output at idle, should be 14.3V or so. If it is below 14V, you probably need a new voltage regulator for the alternator (same regulator is used in Audi, Mercedes, and VW cars, so you should be able to locate one).

Thanks very much for this very informative reply, much appreciated!!!

Take care

[AP 997S]

Also have the cable from the battery to the starter motor checked. I believe there was a Porsche campaign (ie. recall) to correct or replace this cable. Might be a 'high-resistance' or loose connection.

Do a forum search on this topic . . battery cable, starter cable, etc.

Edited August 24, 2011 by AP 997S