Rv Batteries What Size Wire (12-18 Guage) To Use For My RV Battery Run To My Vehicle To Charge It While Driving?

What size wire (12-18 guage) to use for my RV battery run to my vehicle to charge it while driving? - rv batteries

I have an old pull behind an RV trailer (deep cycle) battery, which I bought to run the electricity inside. The trailer does not load on the wiring of the vehicle while driving. I plan to) connect only one wire to a compound in the vicinity of the trailer lighting (rear bumper and run over all power to the battery. I do not know what should I use threads, or is it so important?