07 Duramax 6.6L Battery questions

[jstutz]

My dad bought this truck new in 07. From the time he bought it, he has had battery issues. They just randomly go dead. Sometimes it will go 6 to 8 months and be perfectly fine then usually when winter comes around they will start acting up again. for instance he got up this morning and drove to work. The batteries are perfectly fine. Attempts to go home and they are both dead as a door nail. Initally GM thought they found the problem by disconnecting the windshield washer fluid heater. They found the harness melted and said there was a short in it. He told them he wasn't worried about it and they just disconnected it and pulled the fuse. Well now the problem is back. I have some questions about how the two batteries are connected together. I just assumed they were hooked in parallel with a direct connection. Here is the thing that is confusing me. With the truck off, when the batteries are weak or dead, you read two different voltages on the batteries. One is reading 12.3V and the other is 11.2V. This is impossible if they are tied directly together. Now i think the positive side is tied together through a cable and im not aware of any relay or anything. If this is the case, then to me it has to be a break in the ground connections and they are no longer sharing a common ground. Has anyone out there had any issues like this with this type of truck? also these are stock Delco batteries if it makes any difference.

 

[The motor guy]

If that's the voltage of the batteries then both of them are pretty much shot. 11.2 volts is considered dead completely. The batteries can read different voltages. If you have one good one the bad one will take down the good one. It's like putting one new battery in a two battery flashlight. It will run for a while but then it will eventually kill the new battery. Make sure when you do replace the batteries that you replace both at the same time.

 

[Thermo1223]

He most likely got one bad battery from the factory, hey it happens. Now that bad one is dragging down his good one.

Replace both problem solved or that washer fluid heater had something to do with it. The dealer instead of investigating why just took the easy way out. The harness should be repaired and put back into service to see if it was the root cause.

 

[Scienceman]

It will be alot of $$$ I bet if he replaces both batteries it still may not be fixed. One of my family members has a GM and has had really crazy battery troube to. I honestly think there is just an underlying problem in them.

 

[The motor guy]

If those are the original batteries. Go ahead and replace them. They usually don't last anymore than 4 years anyways and then the fact that they have gone dead several times has shortened the life of the battery. Starting batteries are not designed to go much below like 85 percent charged so it shortens the life if they go dead even once. Only deep cycle batteries are designed to go dead and then be recharged without harm.

 

[jstutz]

I guess i miss spoke. These are not the original batteries. They are OEM batteries. They were both replaced two times now by GM thinking they were just bad batteries. The batteries in there now are less than one year. Also,it is not the same as a flashlight as flashlights are series and these are parallel.

 

[bradepb]

If those are the original batts its time to replace anyway, especially with those readings,check for a draw when you change them.

GM is disconnecting a lot of those heated washer systems it is a recall on many vehichles, recall # 10153 heated washer module short circuit - premanantley disable and remove.

oops they are newer batts, you must have a draw or charge problem

 

[Errtt]

I have never had a vehicle that came factory equipped with dual batteries, but have I done dual battery setup in a few of my vehicles.
I would install the wiring, battery tray, and a battery isolator. Then I would do some re-wire for accessories.
One battery would be the main starting battery and the other would be mainly for accessories. Cranking would run from the starting battery (via isolator), then the alternator would juice to both batteries via isolator. If the vehicle wasn't running, the accessories (I wired) would run off the non-starting battery.
I did this mainly for my off road vehicles, and if camping, would start & run the vehicles every other day to replenish the accessory battery.
When I needed to change out a battery, I would always change out both at the same time.
There were times I ran a few solar panels also sitting on the dash - I took the panels from the boat when I wanted to.

 

[carwreck]

There is a TSB 07033B "BCM Reprogramming for Battery drain" for 2007 GM trucks that might apply to your truck.

Subject: Intermittent Low Battery Voltage, Engine Will Not Crank, Engine Cranks But Will Not Start, Charging System Light On, Service Battery Charging System Message Displayed, DTC B1405 and/or B1516 Set (Reprogram BCM)

This condition may be caused by Body Control Module (BCM) calibrations that create a lower battery state of charge than intended in low electrical power usage modes.

Check with your dealer.

See the gm-trucks forum for more discussion on GM truck battery issues.

http://www.gm-trucks.com/forums/index.ph...mp;#entry607360

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1999 Olds GLS 3.4L

 

[jstutz]

thank you very much. I will check into this.

 

[MrCritical]

Any added electrical accessories to the truck that did not come from the factory?

 

[jstutz]

Well last year there was a brake system and tire pressure monitor for the 5th wheel camper he tow around but nothing initially.I think the TSB fits very well and he is going to talk to the service manager at the dealer he bought it from.

 

[xxch4osxx]

What is the point of a washer fluid heater? I have never had washer fluid freeze even on the coldest days. All the more to go wrong, lol

 

[SteveSRT8]

you won't appreciate that unless it's REALLY cold!