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.

 

[Mogman]

Wow- that Hella switch is a helluva switch!

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

Just be careful on what you settle on, you cannot beat physics, one of the most important things about a high current switch is the pressure applied to the contacts, just as important as the surface area of the contacts, when you crank down on that Hella switch you get the idea.
I have never seen a switch that you could turn on and off with a "regular" type key that feels like it is up the the job.
And of course anything Chicom is pure junk, even the type switch I use to switch the 12V is rated for 500A but if you can find the actual ratings it is only for about 3 seconds, plenty enough for day in and day out use but the day you have problems and have to crank excessively on the starter they can fail and I had one fail like that on a tractor, and that is not usually a great time to add to your problems, The Hella's are not that expensive if you shop around for them.
I am sure there are other switches that are up to the job, I just have not found anything better than the Hella for the money.