Battery wont stay charged

nytahoe · April 27, 2005

Hi everyone,

I am having an el3ctrical problem with my 96 tahoe. the battery wont stay charged. I have had this problem for abou t8 months now. I have replaced teh battery and the alternator since this problem first occured so i know they are good.

Problem is: I charge teh truck over night and it runs rine. Once i let it sit for about 4-5 days, the batt doesnt have enough power to start the truck. i figure there is a higher than normal draw while the truck is truned off adn that is draining the battery.

What is the normal draw on the battery when the truck is turned off?

Any suggestions woudl be greatly appreciated.

Thanks in advance,

chris

snoman · April 27, 2005

What is the normal draw on the battery when the truck is turned off?

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It should be under 100 miliamps and actually under 50 milliamps. YOu may have a sneak or short circut somewhere taking power from system when truck is off.

GM-Tech · April 27, 2005

Technically, GM says allowed parasitic drain on the battery (in milliamps) is the reserve capacity of the battery divided by 4. So a battery with a 100 minute reserve capacity can have a 25 milliamp drain.

In reality, it depends on how you drive the vehicle. Aftermarket alarm systems that I see generally draw around 200 milliamps and it doesn't appear to be a problem on a vehicle that is driven daily. If you let it set for a week, yeah, that could be a problem, particularly if you do a lot of short trip type driving.

Look for things you might not normally notice being on. A glovebox light, a visor vanity mirror that's lighted and not going off when the cover is closed, etc.

71GMC_3/4T · April 27, 2005

I think someone (GM-Tech maybe?) also had said they've seen radios that the display doesn't shut off when the key is off. You might want to sit inside the truck in the dark and look around for anything that is still on that shouldn't be.

Do you have an electric brake controller for trailers? That might be wired wrong.

snoman · April 27, 2005

I think someone (GM-Tech maybe?) also had said they've seen radios that the display doesn't shut off when the key is off. You might want to sit inside the truck in the dark and look around for anything that is still on that shouldn't be.
Do you have an electric brake controller for trailers? That might be wired wrong.

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The first thing I would do though is to check the current drain at the battery with truck off and doors closed and lights off. If it is at 100 miliamps or more, you have a problem with leakage. If it is well under that then you may have other problems instead.

Bullethole · April 27, 2005

I had an underhood lamp with a mercury switch that got bent out of shape and stayed on all the time. Took two weeks to figure it out.

nytahoe · April 30, 2005

OK...The saga continues....

in the past if I use a slow charger and charge the truck for 12 hours, the battery would be fine. I did that again a few nights ago, removed the positive lead from the car to the battery, hooked up the charger, to the pos terminal, found a good ground and let is charge for 12 hours @ 12v, 6 amp. I finally got around to trying to start the truck 2 days later. In that time the battery sat in the truck with the pos lead disconnected, but the ground still attached. When I went to start it, the battery was only reading 9V and it could barely make the door buzzer sound.

What is going on?

Is the battery shot?

could the ground be my problem?

Thanks again,

Chris

GM-Tech · April 30, 2005

When I went to start it, the battery was only reading 9V and it could barely make the door buzzer sound.
What is going on?

Is the battery shot?

Yeah, sounds like a battery.

mmmikkke · April 30, 2005

When I went to start it, the battery was only reading 9V and it could barely make the door buzzer sound.
What is going on?

Is the battery shot?

Yeah, sounds like a battery.

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Not just maybe, but definitely, the battery's shot.

So *now* you should think that maybe you got a defective battery, or maybe your charging system is cooking the battery while you are driving the truck...

71GMC_3/4T · April 30, 2005

I had a battery that shorted a cell while it was on a charger. The charger saw 10V, wanted it to be 12, and nearly blew up the battery trying to charge it. I raised the hood, smelled something hot, looked at the swelled up battery, and backed away quickly. My charger was smokin' hot (still works 8 years later though!) and the battery was sizzlin'.

I agree, there might be something wrong with your charging system. Check the voltage across the battery while it's running at 2000 RPM. It should be around 14.5VDC at the most.