Start battery voltage to rear, with out ACC on

[schanmala]

so has someone put a double gauge in ? Not sure why you would run crank to back it makes no sense , in the front yes makes good sense to know what's going on .
As long as you've got a battery isolator .

I have an isolator and the solar regulator chargers the aux and the crank if the aux is full.

I normally hang out the back of the car when camping. It's handy to see the condition of both batteries with a quick glance