Not to be judgmental, but with such a modern design boat it appears your battery charging system is from the pre digital era. A hard wired, dedicated on board "smart" charger is what you should be thinking. You might also want to upgrade to larger batteries. My 1977 27 footer, for instance, has 2 Costco wet cell, group 27 batteries that are maintained with a 20 amp Tru Charge 3 stage smart charger. It's literally plug and play. It is able to handle 2 separate banks, I have a house bank and a motor bank. I normally get 42 mos, or more from these basic batteries.
My system was installed by the previous owner, probably in the early 90's... I acquired the boat in 99, have never had a problem.
There's a lot of savvy electrical people on this forum that I'm sure can give you some awesome, specific advice.
But honestly, and I mean this in a very encouraging way, now is a good time to upgrade the whole system.. charger, larger batteries and a proper shore power system installation. Good luck.