Zinc air batteries employ oxygen from the air to use in its cathode, and use an anode primarily composed of zinc and an alkaline electrolyte. It produces electrochemical energy by using oxygen straight from the air. Oxygen becomes the cathode reactant, and is diffused directly into the battery. The air cathode uses an aqueous alkaline electrolyte to catalytically promote the reaction of oxygen. The cathode is compact, yet at the same time has an almost unlimited capacity, and achieves high energy densities due to the additional volume available for the zinc anode. The advantages of a zinc-air battery include flat discharge voltage, safety and environmental benefits, good shelf life, and low cost. Zinc air batteries are used for such things as hearing aids, pagers, and medical devices.