Battery charger deep cycle batteries and desulfiting?

Different chargers do different things. I bought one multi-stage charger that plugs into 120VAC. It will go into float mode, and stay there indefinitely, even if the batteries start discharging.

The Battery Minder is a decent unit, and it charges/maintains SOC by using electrical pulses which minimize battery gassing. They are expensive, but one gets what one pays for.