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Discussion Starter #1
Hello All,

I have a 2004 Chevy Silverado 2500 HD duramax extended cab. I've recently found the batteries dead in the morning after sitting all night. Once jumped, it runs great and starts no problem until it sits, which lead me to find the 4 amp battery draw with nothing on, no head lights, interior lights, nothing noticeable.

I've even hooked up my ammeter and pulled every single fuse in all 3 panel locations trying to find the circuit causing the issue with no luck. I've narrowed it down to the draw being before any fuses. The positive battery cable goes from the drivers side, to a connection block for the alternator then takes off else where (not sure where). The other battery on the passenger side, which I'm guessing is the starting battery's 12VDC+ cable takes off underneath somewhere as well.

I'm looking for an electrical schematic of the main 12VDC distrubution wiring so I can further troubleshoot with my meter. Once I get that diagram I can see where the 12VDC+ wires go and I can further narrow down the issue.

Any help is greatly appreciated as I'm tired of waking up to dead batteries, especially seeing as how the batteries are fairly new.

- Tex
 

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I'll ask the obvious,, how old are the batteries? The batteries are connected in parallel to give AMPLE amps to the starter. If one battery is old and weak, it drais the other.
(edit, I just caught the mention "they are fairly new",, here in the desert SW 2 years on a cheap battery is good,, 3+ is a miracle,, a top dollar battery seldom lasts 4-5 years here. The change from hot to cold / cold to hot usually takes then out. Also a AGM battery like the Optima red or similar is a POOR choice for a truck battery. They do not absorb amps at nearly the rate a normal wet cell LA battery can. Hard on the alternator, and leaves batteries less than fully charged)

I'd first take BOTH batteries and have them load tested. If one is down, REPLACE THEM BOTH. To avoid electrical issues in these trucks replace the batteries as a PAIR.

Second have the alternator tested at a good electrical repair shop. The bobo's at the discount parts houses with a meter usually know LITTLE about what the equipment is telling them, and it won't tell you much ON THE TRUCK anyways

Third,, what aftermarket equipment is there??? If there is a retro-fitted alarm and remote start or a hacked audio system by a 10th grader working as a stereo installer, you definitely need to start there and search for all power wires that could connect to EITHER battery ans the positives are connected at the starter.
 

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Discussion Starter #3
To be honest I may have only changed one of the batteries last time, so you could be right in the fact that one of the batteries is draining the other. The reason I also believe that to be true is because like I stated above I narrowed it down to the power draw being before any fuses. I'm electrician and have tested the alternator already, so the only other stop for the 12VDC+ battery cable is the junction block, and the starter, and between both battery + posts. So the only logical explanation is that battery on the passenger side is draining the drivers side battery.

I'll confirm this today when I hook up the batteries. Once I see the draw I'll unhook the 12VDC+ from the passenger side battery, if the draw goes away then I know the battery is weak and I'll replace both batteries this time for sure. I'm positive the starter cannot drain anything because its just a positive connection to the starter solenoid dry contacts so theres nothing that could be draining there.

I appreciate the help!
 

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Not a good habit to drop the + cable, - is a better choice to take the batt out of the loop for testing.

By the time you find one in the pair is toast, it's already weakened it's twin. Leaving that weakened twin in service with a new batt installed....it will now do to the new one what the old one did to it.

In other words, you could wind up continually replacing the oldest of the twins, every 3-6 months. Instead of years for the pair.

Most stores will load check 'em for free.
 

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Discussion Starter #5
Classic electrician, we're so used to AC so we always disconnect the hot wire first. Makes sense to disconnect the negative as theres no chance of shorting anything out! As soon as I took the passenger side battery out of the circuit, the draw went away. I looked at my history for the last time batteries were bought for my duramax and they cant even find it. They're guessing at least 4-5 years was the last time they were replaced.

I'm going to buy 2 new batteries and install them and make sure the issue is solved. Even if it isn't solved I've at least eliminated the batteries as a possiblility. However, I'm fairly confident that is the issue.

Thanks again for the help!
 

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Classic electrician, we're so used to AC so we always disconnect the hot wire first. Makes sense to disconnect the negative as theres no chance of shorting anything out! As soon as I took the passenger side battery out of the circuit, the draw went away. I looked at my history for the last time batteries were bought for my duramax and they cant even find it. They're guessing at least 4-5 years was the last time they were replaced.

I'm going to buy 2 new batteries and install them and make sure the issue is solved. Even if it isn't solved I've at least eliminated the batteries as a possiblility. However, I'm fairly confident that is the issue.

Thanks again for the help!

i suspect that will fix your issue, if it does not, i have a detailed guide i wrote for doing charging system testing if you search posts ive started (theres not that many). The batteries as they age increase in internal resistance which can lead to a parasitic load, especially if only 1 battery was replaced.
 
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