Just an update to beat this horse to death. Since my house bank is also 2 4D batteries, and are only two years old, I decided to transfer one of them to the engine start battery position until it dies, then it will be replaced by a smaller one. 2 new GC batteries will go in the house bank, switchable to parallel the 4D if needed. We use very little power on the hook: the fridge, led anchor light, and maybe a few led cabin lights. I'll keep that spare 4D on a trickle charger when not in use. When it goes, I'll replace the whole house bank with GC's. Whole point of this exercise is to make the batteries easier to handle and have a true deep cycle house bank, while using up what I have.