again, have you had this battery load tested or NOT??
as a GOOD battery should NOT go dead after running a while?
it should be able to handle a discharge for a pretty long time as this atv doesn't come OEM with a ton of electronic's on it to drain it that fast
if a NEW battery has bad cells, it will discharge FAST, the amount of juice sucked down to start it the first time, might be all it has
so, just cause its NEW< doesn;t mean its GOOD battery!
you need to rule it out 100% before moving forward here!