You need to use the correct type of charger for the type of batteries you have. Some chargers cannot/will not/should not be used with AGM batteries while some can be used on AGM/wet/etc.
Get a smart charger, most are these days but not all. You want a maint mode if you plan on leaving the charger hooked up to the batteries whenever the boat is at the house.
Google can be a good friend to teach you lots about batteries & chargers.
GO BIG ORANGE !
I meant to behave, but there were just way too many other options available at the time.