Battery drain overnight

chris_kucia · November 14, 2005

Two weekends ago, I finished up the pre-winter maintenance on my truck.

As part of that, I changed the alternator. Mine was working fine, but the bearings were groaning. Against my better judgement, I used an Autozone replacement, which is reman'd by Palladium. The reman has GM-cast case on it.

While I was working on it, I had the doors open and the radio on and when I went to start it, the battery was nearly dead. Put it on the charger. No problem.

Next day, it was a little hard to start - just an extra crank when starting and a little hesitation. Over the last two weeks, its gotten progressively worse to where now it won't start in the morning.

Thought it might be the battery (which is the original), so I swapped in my Optima red top from my other vehicle (which is also a couple of years old).

Same symptoms. Charge it up - truck starts fine while I'm driving it. Let it sit overnight and the battery's too dead to start the truck.

Put the OEM battery back in and charged it last night. Dash voltmeter read 13v with the engine off (and the charger disconnected). Got up early this morning and it was back down to a little over 9v. Fast-charged it while showering and it started up OK. Probably going to need a jump to get home unless I can go out to the parking lot every couple of hours and start it to top off the battery.

I'm not ruling out that both batteries are past their useful life, but both of them discharging overnight leads me to believe I have some sort of parasitic loss.

Going to put a meter on it tonight and see if I can isolate the problem. My primary culprit is the new alternator, but that could be a coincidence.

My question:

As I understand it, I need to disconnect the negative off the battery and put the VOM into the circuit between the battery and the negative cable. Then, I need to start pulling fuses until I can identify the draw (assuming one registers on the meter).

Is this the correct procedure - I'm more of a mechanical guy than an electrical guy?

Thanks in advance.

Wingnut · November 14, 2005

If the alternator were bad, the truck would die even after you got to tooling down the road. Fuel injection takes 'lectrwicity.

Just as a quick fix to make sure that you can get home today...If I were you, I would run out there and disconnect the battery until you're ready to leave for the day.

asepgrad98 · November 14, 2005

thats a good way to do it, if you have a test light you can use that instead of a VOM. If the light does not light up it isnt enough draw to worry about.

chris_kucia · November 14, 2005

If the alternator were bad, the truck would die even after you got to tooling down the road. Fuel injection takes 'lectrwicity.

Just as a quick fix to make sure that you can get home today...If I were you, I would run out there and disconnect the battery until you're ready to leave for the day.

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Good idea. Thanks.

Could the alternator have some sort of a short in it that would be causing the draw overnight? I'm reluctant to believe its coincidence. OTOH, its been colder lately, and maybe the batteries are weak. I drive the truck daily, so as long as it started with a strong battery, I wouldn't have noticed the draw.

Butch 02 Denali · November 14, 2005

Drive back over to Autozone and have them do an alternator charge test. (Don't tell them you didn't disconnect the battery when you put it in!) Sounds like the rebuilt is NG. Disconnect the battery before you swap the next one!

chris_kucia · November 14, 2005

Drive back over to Autozone and have them do an alternator charge test. (Don't tell them you didn't disconnect the battery when you put it in!) Sounds like the rebuilt is NG. Disconnect the battery before you swap the next one!

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I did disconnect the batterry before putting it in.

I had the doors open and radio on while doing lots of other things, but while I was changing the alternator, it was all buttoned up and the battery disconnected.

jhm · November 14, 2005

Sounds like a bad alternator. I have seen rebuilts go bad soon after install. Autozone is good for some things but I would be hesitant about the alternator.

bronyaur · November 14, 2005

If you have an amp meter, you can check the system to see if there is anything draining the battery. With the key off you shouldn't see anything more than an amp or two (at the battery)caused by the dome light and maybe a light under the hood. Turn off the dome light and drop the hood enought for the light to go out, and your amp meter should show less than one amp. Anything more, and something is either turned on or shorted out. If all is OK, then I'd check the battery.

What you are describing happened to me once and it turned out the radio had a short inside and was drawing 9 amps all the time. Replaced the radio and the problem was solved.

Yukon04 · November 14, 2005

Parasitic load should be no more than 10-40mA. Any more than this and you have a problem. Use a quality ammeter. Your proposed process is sound. Try it and let us know..

chris_kucia · November 15, 2005

Parasitic load should be no more than 10-40mA. Any more than this and you have a problem. Use a quality ammeter. Your proposed process is sound. Try it and let us know..

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I have a VOM with amp readings. Hooked it up and got no reading at all.

Wasn't sure if that was all that accurate, so I hooked up a test light.

The light would illuminate if I had anything on - dome light, parking lights, etc.

When everything was off and I connected the test light, I got a brief illumination (about 1 second) and then the bulb went out.

Not sure if that was the BCM waking up and then shutting down, or a parasitic load that was drained by the bulb lighting. I supposed if the bulb was enough to drain it, then it wasn't enough to drain the battery.

Before I went to bed last night, I checked the archives. There was a post about the alarm system draining the battery overnight. It was too late to do anything else, so I left the doors locked with the inside switch.

It started this morning, but was still weak.

I decided to order a new battery last night from Advance and should get it tonight - yesterday I disconnected the battery at work and when I went to go home, the battery was still pretty weak. Even if it isn't the root cause, I don't want to go into winter with a weak battery, and mine doesn't seem to hold a charge very well anymore - perhaps its been damaged by the constant draining and charging over two weeks (and its 5 years old anyhow).

I'll post more tonight or tomorrow when I have more info.

Yukon04 · November 15, 2005

ALL vehicles have a parasitic load (quescient current). Either your VOM is not accurate enough to read, is broken, or your hooking it up wrong. Try the positive cable and the negative cable.

The GMT900 trucks coming out soon are rumored to be less than 15mA parastic load. That's pretty good considering all the stuff that's in them.

What kind of meter are you using?

asepgrad98 · November 15, 2005

since the test light is not staying lit sounds like a battery or battery terminal problem. the side post terminals can have poor connection and the bolt be tight

Leadfoot 83 · November 16, 2005

I had a serious 'dead in the morning' problem with a '96 S Blazer.

Wife and I could go to town in the evening, come home and park in the garage...everything was OK. In the morning she would go out to take our son to school, and the battery was so dead the dome light wouldn't even come on.

The Blazer was still under warranty, so she called the dealer...they sent out the rollback, and took it in for 'diagnostic evaluation'...LOL

And of course, they said it was the battery, and of course again, THAT was out of warranty. So in went the new battery........3 days later, same problem

So they took it in again, and then blamed a 'vanity light' in the passenger side sun visor for having a draw........they recharged the battery, and we picked it up. And wouldn't ya know it, 4 days later, it's dead again.

So that time I called the dealer....when the Service Manager said "Well maybe your wife is leaving the lights on...you know how women are"...I went off on him!

Once they put an experienced mechanic on it, he found that the Diode in the alternator was bad, and letting the battery fully discharge over night...note, the whole time we were driving it, the Volt Guage in the dash was 'normal'.

You might just have the same problem.

chris_kucia · November 16, 2005

ALL vehicles have a parasitic load (quescient current). Either your VOM is not accurate enough to read, is broken, or your hooking it up wrong. Try the positive cable and the negative cable.

The GMT900 trucks coming out soon are rumored to be less than 15mA parastic load. That's pretty good considering all the stuff that's in them.

What kind of meter are you using?

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Its a Craftsman VOM. I've never used it to check amperage before, but I put it in line between the positive terminal of the battery and the positive battery cable.

When I put the test light in the same place, it came on and went off very mechanically and was repeatable if I waited long enough between connecting and disconnecting.

I kept the light connected for about a minute to make sure there wasn't some sort of pulsing draw and the light would only illuminate once. If I waited about 15-20 seconds before connecting again, I could get the bulb to light and then go out. If I connected, disconnected, and reconnected sooner, the bulb wouldn't come on.

In any event, I replaced the battery with a new Optima this afternoon, and just drove to another city two hours away. I have an hours' worth of work, then a 2 hour drive back and then the truck will sit overnight again.

I'll see what happens in the morning.