When I run the diesel motor the windlass battery in the v berth is charging at 16.4 volts. It is being fed from the alternator to the v-berth (37' boat) via 8w wire. It does not seem regulated and is not hooked into the wind/solar system. My guess is that the wire is not thick enough and I need a regulator. I read somewhere that in this type of arrangement you can get away with a less thick wire, e.g., alternator to battery:far run.

How unusual would it be for this wire not to be regulated? - if so, I should be doing a good job of frying the battery - is there an inline regulator I can use and should I beef up the wires?