So basically, the 9 Hyper Beams of energy aren't the only type of energy in the game. Like people, Pokemon get tired. The typical pace of battle is two moves per Pokemon per round. However, every few rounds, they will get tired and require a "break," during which you can use either one move or two low energy rules (totaling about significant or less), though the latter part is largely ref's discretion. You also have a set number of three-movers going into the battle. I believe it's 1 per side in a 3v3 or less, 2 per side in a 4v4 or more.