I Think I Just Bought Way Too Much Battery

I think there is a standalone converter directly connected to the battery and I can hook shore power to it, so I can upgrade that whole set of wiring to push the 100A without worrying about the wiring through the whole rig. In terms of where the batteries are they're AGM and I have them in a closet (close to the ventilated compartment the existing marine battery sits in). I was thinking that with a controller + temp monitor I should be fine.

Trying to respond to the other comments but the post is failing for some reason.