Get the one from Harbor Freight. ~$5 on sale. They seem to go on sale every other week. I have one for the Vette and one for the RK. If you want to use the hanging plug that goes to the battery, you will need to buy the opposite plug try Radio Shack or an automotive store. Cut the alligators off (be sure to mark the positive wire which will be the red alligator clip) and solder and heat shrink the new plug on to the wires. The un-insulated connection on the charger will be the positive lead.
Remember this is only for keeping the fully charged battery charged and ready to go. It will not charge a dead or nearly dead battery.
Trust me, these things are completely fool proof and will not harm your battery. If you are a (careful) tightwad like me, this is $ well (not) spent.