FWIW, here's my take:
If you always camp with electric hookups, all you need is a lawn tractor battery for the brakeaway on the brakes plus a light or 2.
For one overnight, a standard G24 battery if you use lights sparingly. A G27 or G29 battery is only a few $$ more but you'll probably need a bigger battery box ($15.)
Multiple nights off the grid - now you're into 2 G27, G29, or G31 batteries or 2 6V golf cart batteries. To stretch it out you can go solar / generator, and LED lighting.
I had 2-G27's in our HTT and an upgraded converter.
