first welcome to the site
when you say NEW battery, and you charged it before installing
did you follow the correct way to charge battery, as many battery's that need charging, need to be very low amp slow charged , and NOT on a basic auto battery charger
a regular battery charger can over charge and RUIN a brand new battery!
NEXT, did this atv start before on old battery and you just got a new one due to old one being weak?
or , did it never run.start off a battery ??
I would check connections and POWER at the starter , if it USED to start wit old battery and just doesn't with new one?
you could have a BAD starter here!