It really doesn't matter how many amps that you throw at a battery, It will only absorb it so fast. It takes hours to charge a battery that is 75% charged and sometimes days to charge a battery that is at or lower than 50%. Your best bet would be to install an onboard charger and when the boat isn't in the water, it is plugged in and charging. This will insure that you leave the dock fully charged every time. An on board charger is usually the first thing I installed on every boat i have owned