A AA battery is a single celled device that contains a chemical reaction that can produce an electric current. This chemical reaction is caused by the movement of electrons between the positive and negative electrodes within the cell. The amount of energy that is stored in a AA battery depends on the size of the battery (which determines the surface area of the electrodes), as well as the type of chemicals used within the cell. Generally speaking, a AA battery will contain around 2000-3000mAh of energy.