Im working on a dual battery setup and not exactly sure on how to wire it. Im assuming I will need an isolator of some type. Heres what I want to be able to do. The second battery is going to run my roof lights, radio and all my other add on accessories. Im wondering If I can set it up so that I can choose what battery I want to use to start the truck or use both together. So if the main battery wears down from having the headlights on, I will be able to use the second battery to start the truck. Or if the second battery runs down from the radio or roof lights I can use the main batter. If both of the batteries were to wear down enough to not be able to start it. I would like to combine the batteries to start the truck. So if this is possible if someone could post some links to what I need it would be great.

 

running both batteries in parallel should do as you want. Id upgrade all the wiring from battery to ground. block to ground. from alt to battery. upgrading the wire will allow the extra amperage safely from the paralleling of the two batterys. however i would upgrade yoru alt to one from a silverado/tahoe they use 145 amp ones stock where blazer ones are 100 amp [least mine was] yes that alt from a full size fits thats what i have but i have the 105 amp one

 

yeah run it parallel, so run a positive to positive on the batteries, if it was my truck i would also run a negative to negative cable, you can do it to a ground which relys on the trucks frame to make a solid connection. if you run it neg to neg its a more reliable connection

 

I already up graded all the cables to 0/0 and I have a 145 amp alt. So if I run them in parallel where would I put the isolator? Between the power going between the two?

 

why do you want to use a isolator?

 

i think for an isolator, you would hook each battery up to one side and the alternator to the middle post, and that would isolate the batteries from each other but wouldnt allow you to use both to start the truck

 

An isolator is only used if you want to have the 2 batteries separate which I think is what you were wanting to begin with (ie: accessories run on one battery, truck on the other).
But having it wired that way wouldn't allow you to switch batteries to the truck without switching wires or heavy duty relays.

The more logical way is wiring them in parallel like Quik said. You won't need an isolator because the charging system will think its only charging one battery. Wiring batteries in parallel ads there amperage together but not there voltage. IE: your still gonna get 12v coming out of the batts but if each battery is 700 amps then now you have 1400 amps to play with

The opposite happens if you wire them in series btw. 24v comes out but at the amperage of one of the batteries. (kinda useless for a car application, but theres you some general electrical knowledge )

 

well if I dont use an isolator that would make it possible to drain both batteries. I would Like to be able to cut a battery out of the system in case I drain the other battery.

 

Throw a Painless battery cutoff on the positive of one of the batteries. Just flip it off to make sure you don't drain it and flip it on when you need it.

 

you shouldnt drain both batterys in a short time. You could go a good bit with both linked together.


before anyone of us gives you any more advice what are you trying to do honestly with the truck off?