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Normal parasitic battery draw..

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Old 01-08-2011, 12:40 PM   #1
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Default Normal parasitic battery draw..

Hi Guys,

Simple one this... I recently replaced the battery in my 1991 944S2 because the old one was continually going flat after about a week (it was only about 3 years old), I am trying to double check that the new battery won't have the same problem.

what would you expect the normal parastic draw on a battery to be?...

Using a multimeter with everything switched off and the car locked i found the draw to be 0.3 amps.

Does that sound about right?
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Old 01-08-2011, 01:46 PM   #2
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It should be much less then that more like 10 times less. Do you have the battery in the boot or in the engine bay? Is possible that with the bonnet up there is more current drawn because of the alarm system. If the battery is in the boot you can just make the measurement from inside the car with doors locked. Usual culprit for excessive parasite draw is the stereo.
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Old 01-08-2011, 03:02 PM   #3
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most the time the door pins for the lights stick or dont release fully. This leaves power to interior lights or power windows etc and it kills the battery. Try pulling the door switches and testing them for on/off function.
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Old 01-09-2011, 09:03 AM   #4
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Originally Posted by xsboost90 View Post
most the time the door pins for the lights stick or dont release fully. This leaves power to interior lights or power windows etc and it kills the battery. Try pulling the door switches and testing them for on/off function.
Even easier is to see whether they switch your interior light(s) on/off. You don't have to pull the door switches to test that.

If they aren't working, it's the power to your power windows that draws the excess current that flattens the battery.

By design, power is supplied to the power windows after you switch the engine off until the door is opened. If a door switch doesn't work, the door open is never sensed, and the power to the power windows persists indefinitely.
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Old 01-09-2011, 10:05 AM   #5
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My amp draw on the '88 is a bit over 9ma.
My amp draw on the '87 is about 8.65ma.
My only draw is the radio presets. No alarm.

Clarks says it can be as high as 60ma That is very high--too high I think.

I use a cheap Harbor Freight VOA meter. Set it HIGH on the amps setting-then lower or you will blow the fuse inside. Just pull one fuse at a time until the number drops per Clarks.

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Old 01-09-2011, 11:37 AM   #6
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After working in auto stereo for over 20 years the found magic number is 5 milliamp of draw. This has always been a concern for anyone who has ever installed an alarm and than parks their car at the airport. If you want to take a 2 week trip anything over 5 ma will usually drain the battery dead. This is why most new cars have a rundown protection circuit that disables all accessories until the unlock command is received from the keyless entry. Bad grounds, has that been said here before? Check them all. If you have just one bad ground you will have a higher than normal draw on your system. Always make sure the battery is fully charged. Not at 20 amps but at the lowest charge rate will give the best results, like a maintainer that puts out 2 or less amps of charge. If it is a lead acid battery, are we still using these, top off the water. Each time a battery is discharged and charged you will loose reserve capacity, hence less allowable sitting time between starts. But again I am sure it has been said but it is milliamp and not amps of draw that you want to see.
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