I know almost everyone here has auxiliary batteries to push their systems, but how did you wire them up?

Did you run an output wire from your alternator to the primary battery, then run another run to your auxiliary(s), or did you run wiring straight from the alternator to both?

Anybody using a dual-battery isolator or relay system, or is it just a waste of time and/or expense?

GM originally used a parallel wiring scheme for its factory dual-battery system, I'm just wondering if that is the BEST way. I don't want to have any adverse effects on the alternator. I just want to do it right.

I use the parallel system. Alternator to starting battery. Pos and neg cables ran back to aux battery in back.

ya just wire the batteries together in parallel and keep the alt on the primary battery.

Remember parallel rules! The voltage will be the same in every branch.

Now the isolator is good IF you will be playing with your car off. The isolator isolates the auxiliary batteries from the starting battery. That way if you accidently drain the aux batteries to much you will not drain your starting battery. That way you can turn your car on and then recharge the aux batteries! make sense.

So if you want to run an isolator setup you have to think about your goals!

Here is how to wire your batteries, this pic also shows the big 3 setup in it!

And here is how to wire a solenoid aka isolator