None of the ATV manufactures make their own batteries that I know of, I can say this with absolute certainty about one manufacturer because I work there.
That being said, it is possible to get some bad ones from a supplier, or possibly it sat in a warehouse either at the distributor or the manufacturer for an extended time before it was installed.
At the company that I work at, when the ATV's are started and ran before crating the battery on the vehicle is not used. A separate 12 volt power source is used for the starting the machines and testing of the lights, gauges etc. In fact at the factory that I am at the batteries are shipped dry with the electrolyte added by the dealer who then charges the battery.
I do not know how the other manufactures do theirs.