In a world gone portable, batteries are key. without those unassuming little power supplies to run our laptops, cell phones and personal digital assistants, we might as well return to the days of paper and pigeons. For as much as batteries offer, though, they still annoy us with their frequent need for recharging or replacement altogether. Lately, the zinc-air battery has been turning up as a new choice of power for handheld electronics, providing up to three times the energy of common alkaline batteries in a more compact package.

Zinc-air cells work like conventional batteries in that they generate electrical power from chemical reactions. But instead of packing the necessary ingredients inside the cell, zinc-air batteries get one of their main reactants-oxygen-from the outside air. Oxygen molecules enter the cell through tiny holes in the top and then come into contact with a positively charged electrode (cathode) made of porous carbon. Water and other molecules already present in the pores of the electrode react with the oxygen to produce hydroxyl. These molecules, and other preexisting hydroxyls, migrate through an air separator to a negatively charged electrode (anode) that consists of a zinc gel. The hydroxyls bond to a zinc molecule to form zincate, which immediately splits into two hydroxyls, a water molecule and zinc oxide, and releases two electrons that travel through a circuit to power a device-usually a cell phone or hearing aid.