Battery dies when the car is not used

[Ads912]

Hi,
I tried to start the 912 the other day and the battery was dead. So, I charged it, drove the car and the next day the battery was dead again. Thinking that the battery was shot and would no longer hold a charge, I bought a new one.....the next day, it was dead. The car runs fine when the battery has been charged and the voltage reading with the car running is over 13v.
So, my question: what would cause the battery to discharge while the car is not in use? The interior lights were not left on. The only thing running with the key out, is the clock, which is normal. The radio is not hooked up.

We had some strange warm weather a couple of weeks ago and everything in the garage was covered in condensation, including the car. Maybe it has caused a short in the wiring?

How do you trouble shoot this?

Thanks!

[C. Clark]

Hello,
Battery discharge is normally something being used that uses the energy stored in the battery. That rapid a discharge mimics lights being left on or possible ignition problem, perhaps a defective switch.... ignition or some other major draw device. Trouble shooting is tricky, and usually measured with a little luck. Start with switchs, igniton, heater, lights. Shorts usually blow up something, fuses hopfully, wires burn up, smell, that kind of stuff. Let us know what it turns out to be.
Good luck,
Chas.

[mcruickshank]

Shouldn't you be getting close to 14 volts out of the generator when the car is running?

It sounds like a voltage regulator or generator problem.

I had the similar problem with another car.

You are getting enough power out of the generator to keep the car running but not enough to recharge the battery.

I would swap out the voltage regulator first.
It cured the problem for me.

-Mark

[WFBowen]

In addition to the above-mentioned advice, make sure you're driving the car long enough to charge the battery. The initial drain from the starter motor takes a little while to recoup and, as you know, generator output is rpm dependant.
A good way to initially check for current draw with the ignition off/doors closed, etc., is to carefully remove each fuse and, on re-installing it, check for a tiny spark. Also, check your underhood light switch and any alarm systems that PO's might have installed. If you're not blowing fuses,a battery on/off switch is a good stop-gap until the cure is found. I know it sounds elementary, but are you sure your cables on both ends and engine/battery grounds are absolutely clean? The humidity situation you mentioned is interesting, as it might be preventing good contact somewhere in the charging system. Mark's suggestion make sense as a starting point in replacing parts.
Hope this helps.
Bill.

[Ads912]

Thanks for the info!

There are 2 fuses with 12 volts through them with the key out of the car. I will check to see what they connect to.

There is a pretty good spark at the battery terminal when connecting the negative battery post, showing a good draw (when the key is out). The spark is still there when the live fuses are removed.

I can trickle charge the battery overnight, the car fires right up, go for a good drive, (nearly 14Volts when car is revved). If the car sits for a couple of hours un-used, the battery will no longer turn the engine over.

There is a heavy voltage draw somewhere. I will test to see what is live (ignition/starter etc.) and post it.

Should there be 12volts to any components (starter/ignition) when the car is turned off?

I will be working on it tonight.

Thanks again.

[jac912]

In the "orange book" Porsche 912 Handbook under General notes the author Mel Kay states "Warning: a very common problem is for the cable conn. at the starter solinoid to come loose, in which case the battery will not receive the output of the generator, EVEN THOUGH the red ignition light will stay out. This cable joins volt reg and cable from battery to solenoid" . A note I found very useful a year ago.

[Ads912]

The problem is fixed. I cleaned up the connections at the starter solenoid and voltage regulator. The battery holds it's charge when the car is not in use. I hope that that gremlin doesn't reapperar.

Thank you for all of your input !