If your coach is stored long term and your onboard power system
does not keep the cranking battery charged you should buy a
battery tender. Period. You can't beat them. I've got one on my
trailer, lawn tractor, motorcycle and tow vehicle.
Battery tenders won't boil your battery dry and they are great for
preventing sulfide build up.
It comes with both clip on leads as well as one you can permanently
attach to the battery with a plug on the other end so you can attach
the battery to the charger very easily.
Just google battery tender or search at Amazon.com