I have 2016 F250 6.7 that has an additional 7 pin receptacle in the bed. I assume most people who haul a 5th wheel use that one versus the bumper mounted one (I have never pulled or examined a 5th wheel set up). But I was wondering if there is a way, either with that power source or changing it to something else, that would allow me to plug my boat's shore power cord in when towing so that I can maintain a charge to the batteries? Right now, my bumper 7 pin only keeps the battery for my trailer brakes charged.

When I am towing we like to stock the 2 fridges with food and keep those on. The fridges run off the batteries. Do people who pull campers and 5th wheels provide power to the house batteries when towing? I do not have dual alternators.

EDIT: I should add, my boat has an onboard battery charging system when connected to AC power. So, I guess the question is, can this system be charged from the truck alternator?

 

you would need a battery isolator to prevent your boat systems from draining you trucks "start" batteries.

a boat shop might have the custom cabling you need.

no you can not run AC to DC charging systems off your alternator....you would need a DC to AC inverter...this would be very messy to do DC to AC then AC to DC again.

as far as campers go...alot of them have appliances that run off AC, DC or propane.

 

You're boat only will use 4 terminals when traveling unless you have disc brakes, then a 5th terminal when backing up to release the brakes. None of those terminals are used to charge batteries.
A 5th wheel or towing trailer, the 7 pin system has one terminal that charges the battery, but only when the engine is running.
You could add another wire off of the 7 pin trailer and run it back to charge the battery, or at least maintain it if you installed a 12vdc charger or maintainer, at the battery.
Never seen it done but always possible. You have sufficient amps from the alternator to do both.
I charge twin, 105 lb each, 12v agm batteries on my 5th wheel without issue.

 

The battery on my dump trailer charges when it's plugged in to the truck. I've never had it die even with constant use for a full day.

I haven't looked too closely at the wiring but I'm sure it would be possible to hook it up how you are describing.