CB is right, I have a battery Box mounted right on the trailer, I have the same wire as above hooked to pos & Neg I charge the battery like twice a year! Always perfect!
My gear has striped and the winch needs repair, so I am using a 2 speed hand winch right now, which is ok now that I am on a slip.
But I like to find the parts and fix mine this winter.
Just a battery box with a piece of ply inside for the U bolts to go thur, I use a bungee to hold cover on, But I know others that wrap a cable with a lock to protect it better.
Has a Sears Die Hard battery inside and it really just needs 2 charges a season!