I have 3 of these--
Battery Tender SUPER SMART BATTERY TENDER JR. from Derby Cycles
Each one comes with 2 cables. One with alligator clips and one with rings to
permanently attach to a battery.
They have them in 6v and 12v. I think the price includes shipping. It used
to anyway. At that price you can afford one for each piece of equipment
that you want to keep charged.
I honestly believe they can as much as double the life of a battery, especially
one that is occasional use only like a boat, RV, motorcycle, ATV, tow vehicle.
My truck still has the original battery in it! I know I get double the life out
of my motorcycle battery. Sheesh how can a little bitty battery like that
cost so much?!?