If you have a battery used in a boat they are typcially 800+ CCA which means they will need to be around the 80Ah or greater. This means you would be operating at the higher side of the maximum performance of the MXS 3.8. If you don't have large batteries the MXS 3.8 is more than capable of charging all types of vehicle batteries and includes the motorcycle mode for the smallest of batteries. All this is performed with the chargers 7 stages. The MXS 5.0 is more powerful at 5A, still with the motorcycle mode but it also includes the Recond mode which is helpful in trying to recondition the boat battery that you never charge often enough.