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Dual battery function

Bob 3500HD

By Bob 3500HD
in 6.6L Gas V8 (L8T)

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Donstar Senior Enthusiast

Donstar

Posted
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I would go to the service department of my dealership and ask to speak with someone knowledgeable on the subject.   If they can't confidently explain the operation of your two battery system, then phone GM customer support to find the answer and to report on your untrained local service technicians!   In my situation, I'd simply need to phone my salesman and he'd find the answers.  He may not be a mechanic but he knows how to keep a loyal client!  I've owned this truck for 5 years and I still expect (and receive) this level of service.

Bob 3500HD Enthusiast

Bob 3500HD

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To confirm what George said I checked the power lead in the 7 pin with and without the 30 amp connection off the secondary battery being connected.  Just like was described, the 30 amp lug off the secondary battery supplies the power to the camper with the battery isolated with the truck off.  Thanks everybody.  I think this is solved.

mkeddie161 Enthusiast

mkeddie161

Posted
Posted
Here is the fuse layout on the starter battery.  The 400 amp goes to the starter.  The 250 is the alternator.  The others disappear into the wire harness 
284A9A5F-B889-4054-B8C0-BC1FB2ABAEF6.thumb.jpeg.391e64315ce0a32a1d234a3d57197de7.jpeg
So the 100 amp that is in that box I would assume goes to the other battery..


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mkeddie161 Enthusiast

mkeddie161

Posted
Posted
I thought it operated as such:

 

Truck off = batteries isolated

Truck on = batteries isolated

Truck running = batteries connected

 

100A fuse at isolator is so alternator can charge second battery (when truck running)

 

30A fuse at isolator goes to 12V+ of 7way trailer plug.

 

I think this means you can drain your second battery with a camper and still start your truck with primary battery.

 

I may be wrong, hoping someone else can back this claim.

 

...i did a little experimenting when wiring in my battery maintainer quick connects (one for each battery). My memory is foggy on those results.

 

That all sounds good to me....I want that setup now tho...mine will basically be the same way tho it has a voltage sense switch to turn relay on and off ....

 

Now u just have to put one of these in so u know where ur battery level is

d727dee3d8bd3477581602f6655d3652.jpg

 

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Bob 3500HD Enthusiast

Bob 3500HD

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I'm just guessing now because the wiring harness is all a big bundle. But it would make sense that the 100A is the 100A at the other end at the secondary battery.  Also, the 175A probably goes to the main fuse box.  There's a heavy gauge line that hooks up there.

Another JR Senior Enthusiast

Another JR

Posted
Posted

Slight topic hijack here.  I have not had dual batteries on my previous trucks, but I plan to order them on a 3500HD next month, primarily for truck starting/operating redundancy when remote camping.  (My camper has its own battery system.)  It looks as though the isolator, fuses, and battery wire gage as delivered by GM are not designed to allow you to start from the aux battery if the main battery is dead.  What do you do in that case?  Physically swap the aux battery to the main position?  Use jumper cables from one battery to the other?

 

Bob 3500HD Enthusiast

Bob 3500HD

Posted
  • Author
Posted (edited)

If you’re not pulling from the truck battery you shouldn’t have to worry.  If so, it draws from the secondary battery and leaves the primary fully charged 

Edited by Bob 3500HD

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