I am currently running a three battery setup. I have just chewed through another battery. I have had so many battery problems on top of heavy personal problems that I have a high concern for ensuring that I can start no matter what. I am thinking of changing my setup over to this schematic. It leaves me with a dedicated Starter Battery (C1). That battery does nothing but start the truck, which in turn starts the charging process. Next comes the Main Battery (C1B). It serves for everything your battery does. It is a deep cycle and can handle being run down better. You leave the key on and walk away with some less concern for example. This leaves the third battery as an Auxiliary Battery (C1C). It is another deep cycle intended for run down application or boosting the Main Battery if it is run down. Combined with the truck running and ignition on under the Automatic Relay they give plenty of power for amps and whatever else.

Do any of you see anything wrong with this set up?

Is there a chance the Battery Isolator will overcharge the Starter Battery (C1) thus killing another one?

(PS. This is not a GM Schematic. I drew it)

 

Do not use battery isolators. Use solenoids. I am glad I asked someone. Isolators cause a voltage drop.

 

Maybe it's not the best idea, but I re-drew it for clarity.

 

This is my current setup.

 

You don't want to have B and C connected together like that. You need separate relays for each battery.

Then, I's suggest one of these for when you need to tie B or C in to get you started.

 

why Stan?

 

If one battery starts to degrade, it will bring the other one down.

 

Sure. But that's like saying if my power is out I can't watch TV. It's only two batteries. Not a big deal.

A simple solenoid switch won't help that at all. You're still connecting the batteries together.
And that manual switch you pictured is even more crude.

 

So, how would you hook in the B and/or C batteries if A was unable to start the vehicle? Dig out jumper cables? That manual switch would be just for that scenario. As far as the separate relay thing, it's only a problem when charging isn't happening. When two batteries connected without any isolation, and one starts to degrade, it will draw down the other battery. Not an issue when charging, but why put the batteries through that? Less charge/discharge cycles means longer life.

 

Between starting battery and aux batteries, I would have a separator just like he's already got.

With a manual switch I guarantee you'll forget to use it and get stranded.

You're overblowing the "degradation" thing. I think it's fine.