How Do I Charge, and Maintain 2 New 6 Volt Batteries???

Okay ... I was gonna put my batteries back on the home charger but since I will have them hooked up while the fridge is running for 24 hours before the trip to get cold I assume in that time the charger will take care of whatever is left in the batteries.

Still kinda not sure about some of this but I get the gist of what I need to do and I will keep my fingers crossed.