Problem is, an RV battery is a deep discharge battery whilst a truck battery is NOT. If you hook a deep discharge battery directly to your trucks 12v system and LEAVE it there, you can (and will) kill it by boiling the water out.

You need to go thru a devise that will limit the charge cycle...... or carefully watch the charge with a hydrometer or voltmeter and when it gets charged, disconnect it.

 

Old thread I know, but..
If your alternator is working correctly it essentially stops charging when a battery is fully charged.
The longest lived battery I've ever had was a Sears Diehard wet cell deep cycle installed as the only battery in one of my Land Rovers. It lasted close to 10 years.
I used of for starting and for winching.

 

Thanks Graywolf, I just got a 79 F250 that has never had a trailer hitch installed they used a ball on the bumper. This is a big help! Thanks.

 

I’m trying to get my wiring straightened out. The trailer lights work great when hooked up to my Pathfinder and all the lights work correctly on my F250. When I hook the trailer to my F250 everything works but the right blinker light. Trying to diagnose. I did find the blinker wire in the tail light plug and I’ve spliced in a wire that I’ll connect to the seven pin connector if I cants find the problem. Anyone with any suggestions, I’m all ears!!