I wired in a Guest onboard charger last year. First I wired the boat for shore power which I did not get when the boat was new (mistake). I wired a GFI outlet at the stern inside near the batteries. The Guest circuitry is all sealed in epoxy so it will not corrode. The charger plugs into the outlet and whenever shore power is connected it is operational. If you leave something on like the VHF your batteries will not be dead next time you come down to the boat to go fishing. No overcharging either as would be the case using a standard battery charger.