Battery runs down, ignition off while setting three weeks

Tiny
BEERTRACKER
  • MEMBER
  • 2001 CHEVROLET CAMARO
  • 3.8L
  • V6
  • 2WD
  • AUTOMATIC
  • 100,000 MILES
I watched the 2CarPros video on troubling shooting drained batteries and it was very helpful. Here is the problem:

the battery runs down with ignition off while setting for three weeks.

I recharged the battery and the car started okay. I checked battery voltage with my voltmeter and engine running: 14.5VDC so the alternator is charging.

The car has three fuse
elay boards so I removed each fuse or relay independently while measuring current flowing into the negative battery terminal with my current meter. Current continued to flow no matter which fuse or relay was removed. The ignition was off.

Another way to see this is to remove the current meter and momentarily remove the neg terminal then make contact and a small spark will jump negative cable to terminal.

So this tells me the battery is being discharged with ignition off by some device in the electrical system. By removing fuses and relays I was unable to find this device.

So how much discharge current is normal with ignition off in my car?

Thanks,
Gary
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Tuesday, April 24th, 2018 AT 2:37 PM

4 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 33,699 POSTS
"Advances" in technology are making your observations give false clues.

First of all, unless specified differently by the manufacturer, the maximum allowable current drain is.035 amps, (35 ma). Chrysler says at that rate, a good, fully-charged battery will be able to crank an engine fast enough to start after sitting for three weeks. Cadillac is one manufacturer that allows up to 50 ma. But they do not guarantee the three weeks.

The next part of the problem is by the mid 1990's, there are computers that need up to twenty minutes to time out and go to "sleep" mode. Until then, they can draw up to three amps. You have to wait for them to go to sleep before you can take current readings, but you must be aware that anything you do to open the circuit, even for an instant, will wake those computers up again. That includes simply switching the scale on your meter for more accuracy.

If your engine starts okay after sitting for two weeks, it is likely you do not actually have a problem.
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Tuesday, April 24th, 2018 AT 2:54 PM
Tiny
HARRY P
  • MECHANIC
  • 2,293 POSTS
What he said. Also, it is possible that the battery itself is just losing charge. This happens as they age. The easiest thing to do is take it to the local parts shop and have it tested. You may have to leave it there, but they will do it for free.
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Tuesday, April 24th, 2018 AT 7:36 PM
Tiny
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Thanks for the information. I rechecked the battery drain current with engine offignition off. Initially the current measured 120 ma then after a couple seconds dropped off to 12-10 ma. The car's electronics are entering low power management state. It appears to be working as designed and I was chasing a false problem.
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Thursday, April 26th, 2018 AT 12:17 PM
Tiny
HARRY P
  • MECHANIC
  • 2,293 POSTS
Well that is good. Glad we could be of assistance. Come back any time.
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Friday, April 27th, 2018 AT 3:37 AM

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