It was running this winter and when I tired starting it this spring it won’t start
The problem is that there could be several issues. It's always smart to start with the most simple causes of the problem and go from there or you could end up spending a bunch of money needlessly.
Okay, you said the battery is new. Are you positive it is fully charged?? Put in on a trickle charger to be sure. New batteries are not always fully charged.
Recheck your battery connections. Use a wire brush to clean the connectors if needed.
Did you install a NGK spark plug? If not, you need to.
Check for a loose connection at the PCM/ECM. I think it's gray in color and is located forward of the seat.
Check the starter motor cable connection. Disconnect it, clean and reconnect.
Since it seems to be dropping voltage it's not likely, but be sure your kill switch if OFF. LOL