What batteries do I need

[Mogman]

That's clean. Where did you install your ground disconnect? I'd like to do the same but haven't settled on a location for it. Would like it somewhat hidden, like in the back of the battery box accessible in the right rear passenger foot well but then again I know myself on how this will play out. I'll get in my truck and yell "Dang it- I forgot to turn on the batteries!" and I'll have to get out, walk around, turn it on, and get back in. So maybe thinking I'll put the cut off in on the front of the box so I can lean over and turn it. I'll have to sit in my truck and do some exercises to see where I can put it within reach but not so it's obviously in sight for all to see.

To fully protect it requires a dual (DPST) or two battery switches, one on the ground cable and one disconnecting the 12V tap. Originally two wires, one to the alt and one to the trans.
I recommend a Hella (rated for 2500A for 10 seconds!) for the ground and the little puny more common switch for the 12V, this also gives you a convenient "key" that can be removed from the ground switch,

 

[LCA078]

Wow- that Hella switch is a helluva switch!

I'll look for a DPST to keep it simple, probably one with a key.