HELP! battery died!

okay, i just purchased a 912E less than a week ago. P/O says he just replaced the battery. since then, each time i go to start the car the battery slowly but progressively has a harder time starting the car. now, tonight, the car wont turn over (i end up haveing to push start the car)

here's the thing, i havent been able to take a voltmeter to it, but i drive over an hour and a half and the car doesnt seem to be running off the battery (nothing gets dimmer) and the headlights brightness doesnt increase with RPM.

i heard about the alternator light being involved with the charging system. which light is that? (the red round one marked 'G')?? i'm planning on swapping out the alternator in the morning, but im open to ANY OTHER suggestions...

also, is there any other Alternator i can use for this car? (from another vehicle, that will fit?)

THANKS FOR ANY INFO...

If you push start or jump the car and it seems to recharge the battery I would think you have a short or some device that is staying on and draining the battery. If after an hour of driving you can key start the car that would imdicate the battery is charging. I would park the car over night with the battery disconnected and see if it starts in the AM. If it does it is not the battery. Also check the battery votage should be about 12.2. With the car running should be about 14 at about 2500 rpms.

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• Joe A.
• 84 911 Targa
• 75 914/6 3.0

PDV,

Start from scratch.

Charge the battery with a trickle charger if you can, a fast charger is not real good for the battery and you want it topped up.

Put a digital VOM (volt ohm meter)(buy a cheap one at Radio Shack or the like) on the battery and check the voltage. Should be 11-12 volts. Start the car, should be 13.5-14.5 or so... a bit high is not a problem as long as its under 15, but not too much lower than 13.5. If the voltage is a bit low, take the motor up to 2000 RPM's or so and the voltage should come up.

If the value is lower than 13 or even equal to the reading you get before starting the motor, then your alternator/regulator is not recharging the battery.

If the value is above 13.5 then start turning things on... like the lights, fan, back window heat and see if the alternator will pull the load. If it keeps the voltage up then you are doing fine, if it drops below 13 or so then its not pulling the load and either the alternator or regulator needs replacing.

Drive the car for a while then do the same checks to see if something is breaking down after it gets warm. Not too unusual for the alternator/regulator to drop offline when it warms up.

If all the above checks out then get the battery checked out. Could also be a short (light left on, or such) that is draining your battery. To check this, charge the battery and then drive the car. Where ever you stop take the negative battery cable off. When you return put it on and continue like this for a few days. If the car/battery works fine like this then you have something in the system drawing it down at rest... not good and a ***** to troubleshoot at times...

If the alternator/regulator is tits up, call around and find a local shop that would rebuild them. Do not go to Porsche as they charge you an arm and leg for the thing. Takes less than an hour to pull it out and same to put it back in, look on Pelican for help on this.

Hope this helps...

JoeA

I just faced--and with the help of John Walker's advice--solved the exact same problem. All of the advice above is good in terms of finding out if your alternator and battery are good. If the battery is good and the alternator is charging, here's the next thing you do. (Worked for me.)

Take the positive lead off the batter post and put a voltmeter/multimeter between the post and the positive lead, with the ignition off. If you see a draw of about 10 volts, it's stuff like the electric clock, radio memory, security system etc, and that's normal. If, however, you see a draw of 11.8 or 12 volts (depending on how fully charged your battery is), you have a dead short somewhere, and that's where your power is leaking out. One by one, remove every fuse and relay in the trunk and engine compartment and watch the voltmeter. If one of them causes the reading to fall to 10 volts (the permanant-draw stuff) or virtually zero, if you've already disconnected stuff like the electric clock, there's the short--in whatever wire(s) is connected to that fuse.

The final thing you do, if none of the fuses or relays pulled solves the problem, is crawl under the car and disconnect the fairly hefty positive lead to the alternator from the starter relay. If that fixes the problem, you've got a bad alternator diode or something of the sort.

Stephan