Problem: battery drains overnight but this is very recent. Prior to last two weeks, it would sometimes take a week (or two!) for it drain to where the car wouldn't start. Yesterday, charged the battery (a fairly recent one) to 12.8 volts. Ran all the battery tests as described in Adrian's book. Hooked up the multimeter in series with the battery. I turned off the interior lights and disconnected the luggage compartment light. Did not find any drain by pulling one fuse after another. Although most posts have said you should get between 50 and 75 milliamps, my multimeter was consistently showing 90 mA, although that is consistent with Adrian's book which says 90mA if the car has an aftermarket stereo, which mine does.

Tonight, 24 hours later, the battery voltage is down to 10.20. Any thoughts beyond repeating the fuse-pulling test?

 

The 90ma is on the high side on the max draw value based on my 964 experience.

Use this as a ROUGH estimate of no-use battery life:

Time (half capacity for good cranking) = Battery Capacity (amp-hrs) divided by 2
divided by Draw (ma)

Example: Assumes a good battery fully charged

Battery Capacity - 60 amp-hrs
Draw - 50ma (.050 amps)

Time (days) = 60 / 2 / .05 / 24 = 25 days
Draw = 100ma
Time (days) = 12 days

 

I've been having a similar problem, now partially fixed. The car was drawing 0.73A, which I tracked down to the engine compartmet light - pulling the bulb, I now get a drain of 80-90mA which is still a bit high. I've tried pulling fuses again, but none reduce the drain. However, if I open a door (interior lights are switched off, no key in the ignition), I can hear a relay click after a couple of seconds and the current goes up to 0.52A. What could cause this?

I think there's an after-market alarm fitted, which is my primary suspect, just need to find out where it is.

 

Dear Richard,
90ma is quite common with these new stereo systems and aftermarket alarm systems. There is a Porsche technical advisory which discusses this issue.
90ma is not going to flatten a battery overnight.
If this is all you are measuring you do not have a drain you have a charging problem or a battery problem.
90ma is too high for my liking as well but it is something that may have to belived with. My current drain is 13ma but I only have standard equipment installed and all non switch systems removed except standard alarm and the DME. There was a hands free telephone installed by the PO which created all my problems.

Dear Ian,
You have something in your system. I recently assisted somebody in Hong Kong with a similar issue. When he looked at his wiring it had been butchered in order to install a kool stereo system. The end result was the complete removal of the stereo system, a total repair of the wiring looms and then the stereo was reinstalled correctly using switched power and not everything running direct from the battery.
The only thing you can do is get in their and take a look. An aftermarket alarm system would also cause similar problems if not installed correctly.
Far too many people are wearing blue pin striped aprons when they work on Porsches and other cars nowadays.
Butchers wear blue pin striped aprons if you need an explanation
Ciao,
Adrian.

 

Thanks Adrian - time to get my head under the dash!

 

Dear Ian,
In the UK you can guarantee that there is an aftermarket alarm installed. Before you get too carried away I would recommend you find it and then locate a wiring diagram for it.
I would start under the right seat and or just behind the right seat. The standard alarm system is located at the rear of the luggage compartment on the bulkhead under and to the rear of the right luggage compartment hinge.
Ciao,
Adrian.

 

Adrian: I finally found the current drain... my glove box was not closing entirely, leaving its light on. Once I corrected that problem, the drain problem went away.