Join Date: Aug 2006
Location: Arlington, VA
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If you're talking only about charging your batteries at dockside only (where, presumably, the time required to bring them to a full charge isn't critical), then the size of the charger isn't a huge concern.
However, what is a concern is the prevention of sulfation of the plates through proper staged charging (bulk, acceptance, float) and, for flooded batteries, periodic equalization (bringing the voltage up to about 15.5 volts for several hours). Some battery chargers have an equalization capability.
The good news is that for relatively little money you can buy a top-notch battery charger which is sized properly for your battery bank. The Iota chargers are very robust, well designed, and relatively inexpensive. They come in several sizes, up to 90A. They use PWM (pulse width modulation) technology and with the IQ-4 smart charge option ($35) will keep your batteries happy and fully charged.