Not dumb,just the most common thing that happens that people overlook. Batteries can charge up and show 12+ volts and most people assume the battery is ok but an open or weak cell can cause voltage to drop like a rock when under a load.

 

I know how you feel. I have the same quad and mine wouldn't start one winter unless I used the pull start. It was a loose battery cable that I overlooked. Sometimes it's the simplest thing and we look at something else more complicated. I'm glad you got it figured out.