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Old 06-09-2020, 01:22 AM   #1
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986 battery drain

Good day guys! I have a 97' 986 which has suddenly been having problems with the battery draining. It's gotten so bad that now it only takes 1-2 days for the battery to drain completely. I've had the alternator checked and was told that its still in good condition. Everytime I turn the ignition off, I double-check that the lights and all other electrical devices are off. If anyone has any suggestions, please let me know. Thank you.

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Old 06-10-2020, 11:12 AM   #2
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Check the current pull on the battery (called parasitic draw) when the engine is off and the everything else is turned off.

Its an easy test to perform: Place an electronic multimeter in series with the battery negative terminal and monitor the current flow. Do this by disconnecting neg battery cable. Then place the positive probe of the meter on the neg battery terminal and the negative probe of the meter on the unattached neg battery cable.

Car should be off with key removed and doors closed and so on - just like it would be if it were parked and locked.

The value measured will be in amps or milliamps. It should be less than 80 milliamps or 0.08 amps.

If the value is greater than that, then you have a short circuit somewhere that is causing the battery to drain quickly. To find the source of the power drain, leave the multimeter in place and start disconnecting each fuse one by one. When the power draw drops to less than 80 milliamps, then you've found the circuit that is causing the battery drain. Look up what components are on that particular fuse circuit and then perform further testing on each component in that circuit (disconnect one by one) to the find the source of the high current draw.
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Old 06-14-2020, 05:49 AM   #3
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One thing I would like to add since I just did this on my 99 is when you open the frunk you have to make sure and unhook the light inside it or it will show up as a draw on the meter.
When I just did this on my P-car it registered 0.025 or 25 milliamps which is pretty good for a car with a lot of dodadds that Porsche has on these cars.
Good luck on finding your battery drain.
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Old 06-14-2020, 09:04 AM   #4
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Quote:
Originally Posted by thstone View Post
Check the current pull on the battery (called parasitic draw) when the engine is off and the everything else is turned off.

Its an easy test to perform: Place an electronic multimeter in series with the battery negative terminal and monitor the current flow. .

If the value is greater than that, then you have a short circuit somewhere that is causing the battery to drain quickly. To find the source of the power drain, leave the multimeter in place and start disconnecting each fuse one by one. When the power draw drops to less than 80 milliamps, then you've found the circuit that is causing the battery drain. Look up what components are on that particular fuse circuit and then perform further testing on each component in that circuit (disconnect one by one) to the find the source of the high current draw.
Make sure you are using the AMP function on your meter, not voltage. You will also find it a small challenge to keep the probes on the battery terminal and disconnected ground cable. this needs continuity to complete the circuits in your car, otherwise the battery is disconnected. Some folks drop vise grips on the terminal and alligator clip to the release lever and alligator clip to the bolt on the ground cable.

If you have a second meter, it is MUCH easier to read across the fuse for voltage, there are little holes in the back of the fuses for this. (slight voltage across fuse shows power flowing, then pull the fuse to quantify related power draw.

This way you aren't pulling fuses, jumping back and forth to your amp meter and you can quickly find circuits that are power draws. NOTE: Some of these power draws are normal.
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Last edited by tonythetiger; 06-14-2020 at 09:12 AM.
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