I have duell batteries on my boat with one being a deep cycle for the trolling motor. Portable chargers didnt work well for me so i installed an onboard charger which is always plugged in when the boat isnt in use. It maintains both batteries as needed.
I might add that i also have a 2000 model slide in camper on my
pickup which is rarly removed. It still has the original battery. No doubt it is no longer any good but so long as the
camper is connected to the pickup wiring harness everything works. Yes it does draw from the truck battery when im using the
12 volt lights in the camper. When the camper is plugged into a 110 outlet it charges everything anyway.
It works for me and it might work for you also. Otherwise id be considering an on board charger.
