2007 Rancher 420 battery drain
batterys can be unruley...they might last for years with being started 5-6 times a year. or drain after a week or so. if you have let the battery die alot, sounds like it, then charge it up and it wont last: the battery is probably bad now. they can be tricky things.
i would try chargeing the battery overnight, not connecting it to the atv, and let it sit for a day. then take a volt meter and check the charge. if its less than like 12v its not holding a charge well. a good battery will hold like 13-14v
i would buy a lawn tractor battery, but thats just me. i would try a new battery before saying its a power drain