Ed, I've attached one half of this quick-disconnect to the battery with ring terminals attached to the cut off ends: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
It's long enough to extend to the small door that can be opened with the top down.
Then, the other half is spliced in to the charging cables of my battery charger, replacing the alligator clips that were there.
I mounted the part that attaches to the battery so that the shielded, female plug is wired to the positive terminal to prevent any accidental short circuits.
Of course you can always plug the trailer's shore power cord into a house outlet using a 30A to 15A adapter, and that will charge the battery too.