https://pokemongo.gamepress.gg/pvp-charge-moves
The PVP move info displayed on the pokemon info screen is wrong, and a bit of a mess. Shadow Ball costs 55 energy in PVP. I'm guessing that anything higher than 50 energy is rounded up to one bar. There is a big difference between Flamethrower at 55 energy and Overheat at 80 energy, but they both shown as having 1 bar.