Trailer Tow Key On Hot Lead

Is the trailer tow, key on, hot lead a regulated charging source. I understand that it can be used to charge a battery that is in a camper or camp trailer, although due to the size of the wire and the length of the run, not a real good source for recharging a low battery.

I want to make sure that if I have the battery at full charge, the key on hot lead will not continue to charge the battery to an overcharged state.

Knowledgeable input would be appreciated,
Doug