the best one is a "Battery Tender", that's the brand name. They come in a .75V that plugs right into the outlet like a transformer, and they be a 1.5V that have a cord that plug into the outlet like a food processor, it is a nicer one and the lessor be about 25.00 and the greater be about 40.00 and everybody got 'em, Ebay, et cetera.
oh, and they has red lights and green lights that tells you the status. mmmm
oh, and if you don't crank your bike at least once a week, keep it plugged in.
oh, i fo'got. they has some wiring that comes wif 'em two big alligator clips and a plug in jack that is the best, let it dangle under the bike