Hustlin' Hank wrote:
I need some ideas. It is a Yamaha atv. Battery shows 12.9 volts and
turns the engine over fine, but won't start. When I hook up a battery
charger it starts right up. Battery voltage when running is 14 volts.

Any ideas?

Hank ~~~knows something has to be wrong

Are you connecting the charger directly to the battery?