AP in Pocket Mortys stands for Attack Power. Each Morty has an unlimited amount of AP for each of his attacks. You can recharge your AP at the Healing Center or by using a Plutonic Rock or Pure Plutonic Rock. Plutonic Rocks can be found, won during battles or at Blips and Chitz or crafted. You can see the crafting recipes for Plutonic and Pure Plutonic Rocks here.