Originally Posted by Toubab
I have a battery charger already that's set up to charge both the house and engine batteries but they're different chemistries so I want to have separate chargers. I've been thinking a lot about my different options and I like this one the best because I think it simplifies things in some ways because I don't have to worry about having one battery being chronically over/under charged or any diodes or anything like that. Plus then I have a backup charger that can be switched to the other bank in an emergency
That's very sound thinking
Have a look at the offerings from Sterling, and from Victron. Both of these make small multistage chargers which would be good for start batteries. Less than $200, I believe.
You don't need much amperage in a charger for a start battery, because the amount of power to be replaced is negligible. The main thing is that it should have a good float mode (Victrons even have a maintenance
mode, where very little voltage is applied, but an absorption charge is automatically applied once a week).