I use one of these permanently installed on my RTV in conjunction with a dash mounted switch and a inline fuse. It serves double duty for the grass seeder and the sprayer. You could also use it with a trickle charger if you desired. Basically it's just like a four wire trailer connection.
Edit... I believe mine has a larger gauge wire.
Enercell 2-Conductor Automotive DC Accessory Cable - RadioShack.com
Edit... I believe mine has a larger gauge wire.
Enercell 2-Conductor Automotive DC Accessory Cable - RadioShack.com