Other alternatives: There are clip ons that look like cloths pins. Require wires from the clip to the battery. Or really old school - lamp wire and alligator clips. One clip to the post of the plug, the other clip to any handy spot on the engine. For either, you need to source a holder for the battery to run the wires from, or solder the wires directly to the battery. Just take care in soldering, as heat applied too long can be detrimental - a higher wattage iron with a big tip helps you minimize the total amount of heat you subject the battery to.