If you don't mind rotating the leads between batteries than a single charger will work. Two years ago I had 4 batteries (two group 31 deep cycle, group 24 starting, and 12v riding mower battery) in my garage that I kept charged all winter with a single charger. Every Tuesday and Friday I rotated the leads to another battery, worked down the line and started over. Never a problem. I still use the Schumacher Ship to Shore charger for my main battery, in fact it is hooked up right now keeping the charge on my motor battery. My Minnkota on-board 10amp dual bank (5 amps per bank) charger is hooked up to both my group 31 trolling motor batteries and is also plugged in right now. No issues there either.
I am debating about pulling the on-board charger and the batteries when I put the boat up for winter and charge them in the garage again. Or leave the batteries in and run an extension cord out to the boat for the winter. Might sell the dual bank charger and buy a three bank charger for next season. Or maybe buy a separate single bank charger for the motor and not worry about RF interference.
HOI Crappie Club
Where family and friends come to compete for a little more than bragging rights.
Quick, someone teach me how to fish so I can win this tournament!!!