This old thread about setting up dual bateries--need explanation

[MarvinVR]

https://www.tahoeyukonforum.com/threads/dual-batteries-installation.100955/ Ok Im not up on that stuff but what if you want one battery to stay charged but ONLY be used by accessories? How about if you want it to be able to start the truck as replacement should the primary battery croak? If both are hooked up and one shorts, the good one would not be able to start the engine.

 

[Joseph Garcia]

I run a two-battery setup, and I use the second battery strictly as a 'just in case' spare. Is this the use case that you are trying to achieve?

The second battery sits in the second battery tray, and I have cables connected to the main fuse plate, prior to the main fuse, and to the engine ground. with high amperage quick disconnects. Occasionally, I quick connect the second battery for a day, just to keep it charged up.

 

[mikez71]

You could also get one of those battery switches that lets you select 1,2, or both.
I thought an isolator was a good idea as well, but decided a parallel setup would be simpler.
Hopefully I'll notice low battery voltages before any starting issues..

 

[j91z28d1]

Google or Amazon search "dual battery isolator kit".

they have many different ones with different options. some of the hot rod guys are starting to use the electric ac compressor hidden to keep. engines clean, run them off a 2nd can battery using isolators so it can be used with the engine off, but only run down the 2nd battery. since they need like 60-70 amps at 12v. it will kill a car battery pretty quickly on its own