You'll need to measure the load on the battery during normal driving to get a sense for what the running requirements are.
I started to measure various electrical loads on my vehicles but only got as far as my Acura. It has a minimum running requirement of 163 watts. I listed all the loads in this spreadsheet under the TSX tab.
https://docs.google.com/spreadsheets...it?usp=sharing
You're going to kill batteries much more quickly, especially if they aren't deep cycle.
You'll want to change out all the lights to LED if you want to get very far at night.