Originally Posted by Rzeppa
I used a big marine battery as the aux battery, and built an entirely separate wire harness just for the Aux system. I charged the aux system through an isolator (low forward drop dual rectifier) I got from an RV place. It worked great for decades, no problems ever. The whole idea is you can run loads to your heart's content from the Aux system and not worry about being able to start and drive. Alternatively, if you pull a
and leave your lights on, you can give yourself a jumpstart with just one jumper cable
This is similar to the dual battery setup I built. I used a Painless solenoid with a 3 way switch. Up on the switch is jump mode, middle is off/normal, and bottom is charge. Every now and then, I flip it to bottom and drive around a bit so it'll get a charge. I have a Blue Sea fuse block wired to the aux battery and then to the switches for accessories: winch, lights, etc. My CB is wired into that as well. HAM is hard wired to the main battery. I've got a couple of 12v outlets in the back that are also wired to the aux battery.
The whole system was pretty easy to put together. Ran about $300 for parts and I found a deal on a brand new Optima for $100. Zero issues except when the negative cable fell off the aux battery a few weeks ago...