Question about 2005 GMC Sierra 2500HD 4WD

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Auxiliary battery use

I have a 2005 GMC HD2500 Duramax pickup, that came with the heavy duty camper/trailer towing package, which includes the camper wiring harness. I just installed a camper receptacle in the side of my truck bed, preparing for a camper I am purchasing. The camper has two "on board" batteries, and it's my understanding that when the camper is plugged into the new receptacle, the truck's alternator will charge them when the engine is running. My question is: "What is the auxiliary battery, that's located on the passenger side under the hood of my truck, used for?" Is it tied into this same system, and will it also feed the camper? Or, is it for something else, like a snow plow attachment? How does it maintain a charge?
Also, I think I will need to install a battery isolator to prevent the camper's 12 volt devices from draining the truck's starter battery, when camping without "shore power."

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  • Anonymous Mar 21, 2014

    Need location of batt. Isolator

  • Greg Scott
    Greg Scott May 12, 2017

    I agree with dwbussell about the second battery since I have owned a few diesel trucks. On another note, having rebuilt part of my connecting cable for the trailer from the truck, there is no direct connection for your camper; it is strictly for your camper lights and brakes. I was? told the same by my sales rep, but later found out, like many, he didn't have a clue. I drained both batteries in my camper and had to connect to shore power to charge the batteries. Now I frequently run the generator.

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The extra battery is there because of the glow plugs and intake heater of the duramax. During cold weather both of these systems draw high amperage from the batteries. A single battery will function, but not as well as a pair.

Posted on Nov 19, 2009

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