[barnacle]

I would go with two batterys. If you do go with one I would go with a dual purpose battery. This is a cranking and deep cycle battery all in one. A battery switch is nice due to if you leave something one it will be turned off when you turn the switch off. Be sure you wire it so you float switch stays hot all the time. THe best way to go is have two batterys. One a cranking battery for the engine the second a deep cycle for all equipment. In a 20ft boat two batterys is overkill but its well worth the first time you need it.