I have an old boat, and i would like to get an on board charger, but i dont want to spend a lot of money. my question is, is there a cheap, or diy way to make/ install something to be able to keep my three batteries fully charged.
currently i dont have very good batteries, and i plan on buying new ones before spring, so i want them to last as long as possible.
what is my cheapest option, to keep my batteries charged correctly?

