As soon as I get home I plug in my on board charger. I unplug them the next day or as soon as I see them fully charged. I have a 30 amp 3 bank 10amps per bank charger which will do my cranking battery and both my trolling motor batteries. Charge time will vary from a couple of hours to 10 hours pending how much I have drained my batteries.

Heat is very hard on a battery. In the summer/hot weather months if my boat sits longer than 10 days I will charge my batteries even if I have not used the boat. Normally they will be full within 1 hour. In the winter/cool weather I will charge them if my boat sits longer than 3 weeks.

Regardless of when or how you charge your batteries it is very important that people check the water level on a regular basis. Low water will create heat while charging and heat is the number one killer of a deep cycle battery. A good deep cycle charger will charge in stages. Stage 1 will be a low amp charge for a small period then increase to a high amp bulk charge, that is followed by a low amp charge. Then the final stage will be a trickle charge.