I bought an Ariens 46" riding mower,brand new,last month. Got it home ,started it once,then wouldn't start after that. Called Ariens,and they sent a local small engine repair guy,who is an athorized service repairman to the house,picked up my mower. The battery was the problem. He replaced it ,and brought it back to me. No problem now.
Excellent service from Ariens,and the repair guy.
Anyway, Just cause it's new,don't mean anything with batteries. Get yourself another one,and I bet you'll be good. They are not that expensive if yours isn't still under warranty.
By the way, I charged the original battery,and it still didn't start. Even with the charger saying it was full charge.