12 volt supply

The electric current hook up is going to be either 30 or 50 amp. The plug on the end of the cord is different and you can buy adapters to connect 50 to 30 or to 20, etc. Your tow vehicle (TV) must be running or have the key on to supply power to the RV battery. While running, the alternator provides charging to the RV without draining the TV battery. With just the key on, you could drain the TV battery and that is not recommended.
Your RV battery charges while plugged into AC at the campground or at your home, or while driving down the road. If you camp without hookups, you need to be energy conscious or have solar and/or generator to replenish the battery. Also when camping without hookups, you can only use the 12v items like most lights, furnace, landing gear, etc, but not AC, microwave or television unless you have a special setup like a large battery bank with lots of solar and an inverter.
The amps you mentioned are only supplied by an electric outlet connection. You fiver will have a charger/converter that charges the batteries and converts 120AC to 12v DC when plugged in to the electric outlet. Otherwise, the 12v DC is provided by your battery bank.

Here is some MUST READ material for you:
The 12volt Side of Life

Excellent response! I think you pretty much said it all.

What I will do if I'm leaving the TV hooked up is to unplug the trailer from the TV. I'm a believer in Murphy's Law, if it can happen it will happen. It shouldn't be a problem but this prevents it.

how new or old is the fifth wheel? It should be 30 or 50 amp as stated. I too always unplug from the truck even if I leave trailer hooked to truck over night

To answer your question, it depends on the make of your tow vehicle.

If you have a RAM or GM product then yes, the battery in the trailer is directly connected to the battery in the vehicle and the trailer can run the trucks battery down.

If you have a Ford product then there is a relay that separates the two batterys when the vehicle is not running so one will not drag down the other.

The 40A line is somewhat current regulated just by having too small a wire to provide that much current. If the trailers battery were flat dead or shorted then it may blow a fuse in the truck - but that is the exception. Normal charging from the truck wont go near 40A because of the wire size.
There is also usually a breaker in the trailer that limits current draw (but not always).

Did a trailer salesman say it is "40" amps? They sometimes have a little trouble with true facts as opposed to the other kind.


The 12 Volt Side of Life is a real good place to start.

Folks, the OP is talking about a 40A charge supply from his trucks battery (which is a common rating). He's not talking about the AC supply.

ScottG wrote:
Folks, the OP is talking about a 40A charge supply from his trucks battery (which is a common rating). He's not talking about the AC supply.

yup, you are right. I figure it like a trickle charger when towing and I use a battery charger when I have electric or leave plugged in to 110 when I can.

My Truck is a 2006 Chevy 2500HD and I am looking at a 2002 Thor Tahoe 22RK. I am buying the Trailer from a private party who was said nothing about about the battery of the Trailer other then it is useable. Thanks for the info, it confirms my thoughts. I can drain my Trucks battery dead. For those wondering in my Truck there is a fuse listed as Stud #1 that is the fuse for charging the trailers that goes to the plug on the bumper of the Truck.

Generally you will unplug from the truck while camped.
If the truck is running the trailer will not discharge the truck battery.