Help understanding dual battery setup

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99Sierra

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When I purchased my '99 Sierra, it was equipped with a dual battery setup. I'm assuming the previous owner did this when the winch was installed. I've also read here that a dual battery setupo could be ordered from the factory as well. I'm trying to understand how this all works but I'm a bit confused. Here's a diagram of what I see under the hood:

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The negative terminal on the left battery is grounded, and a second wire from the negative terminal runs to somewhere near the exhaust manifold on the passenger side - I can't really see where it terminates. There are three wires coming off the positive terminal - one to the alternator, one to the fuse box marked "Fuse Relay Center" on the driver's side, and one to somewhere towards the front of the engine block. Again, I can't really see where this terminates.

The right battery also has a ground coming from the negative terminal, and positive is wired to the Fuse Relay Center box. The winch is also hooked up to this battery.

I'm just not sure what I'm looking at with the unknown wires coming from the left battery. My best guess is the unknown negative wire on the left battery is going to a ground elsewhere, maybe the frame? Not sure what the unknown positive wire is. Does this look like a typical dual battery setup or could someone shed some light on this type of setup?


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Big D

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You need Power to the Starter, im sure you'll find your 2 in question there.
 

kennythewelder

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From you drawing, the left battery is your normal battery, just like any other truck would have. The right battery is there to run the winch. It is tied into the fuse relay ctr so that it will be charged from the alt. My best guess, is that the right battery is only there to run the winch and nothing else, but I can't say for sure, without you tracing the wires that are inside the fuse, relay ctr (fuse block) to see where they go.
 

kennythewelder

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Also the 2 wires that you have on the left battery with ? on them are, The black is your main ground wire. It is tied into the engine block, and the red wire, goes into a pipe for protection, follows the block, and is tied into the starter.
 

88GMCtruck

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Chances are someone added the driver's side AUX battery. Likely it's just tied into the electrical system at one on the power studs at the fuse center because it was clean/easy.

Factory dual battery setups use an ignition switched isolator which would be mounted on the fender next to the fuse center. It runs power from the fuse center to the solenoid and then to the battery, so basically what you have not just sans the solenoid.
 

Dr.Zoom

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What gauge wire was used and how many amps does the winch draw? Got a pic of the connections at the fuse/relay center?
 
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Gambles

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Unless the driver side has some sort of isolation they pretty much just share the load, I set mine up similar I just used a 1 in 2 out to 0 gauge between the alt and pass battery in your picture, and 0 gauge grounds to block body and frame from both batteries, makes my 3000 watts and max Ac with the headlights not even budge the volt meter, used to rest at 13.4 driving and like 11.5 if I was stopped, and no ac... Now 14.4 with ac and music bumping sitting idle.
 

Justin S

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Unless the driver side has some sort of isolation they pretty much just share the load, I set mine up similar I just used a 1 in 2 out to 0 gauge between the alt and pass battery in your picture, and 0 gauge grounds to block body and frame from both batteries, makes my 3000 watts and max Ac with the headlights not even budge the volt meter, used to rest at 13.4 driving and like 11.5 if I was stopped, and no ac... Now 14.4 with ac and music bumping sitting idle.
Some of that can be credited to the alternator too, i'm assuming you upgraded that as well?
 

Gambles

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Originally went to they 145 or 165 454, don't remember was like 3-4 years ago, but the voltages were all with the same alt.
 

99Sierra

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Thanks for all the replies and helping me figure this out.

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Most likely this previous owner added the second at the time the winch was installed. Both batteries are connected from the positive terminals to the same point on the fuse relay center box, here's a pic:

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I don't see any battery isolator so I guess both batteries share the load and would be drained equally? I'm assuming I could pick up something like this so I can use the driver side battery to power the winch and other accessories without worry of draining the main passenger side battery:

http://www.amazon.com/Stinger-SGP38-80-AMP-Battery-Isolator/dp/B001HC6UJ0/ref=sr_1_5
 
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