Yes, zinc-air (so called for its negative zinc electrode and positive "air-breathing" carbon electrode) is a throwaway battery, as with typical primary cells, and its use may be puzzling to some. Overshadowing that issue is Zn-air's capacity to deliver energy, said to be several times that of lithium-based types.

Zn-air also fits right in with the way applications are going. Besides cell phones, there are now ultra-intermittent-service applications where the battery must provide fairly high currents for 5 to 30 minutes a year. Additional factors include the perceived limits of the various electrochemistries in squeezing out more power safely and within environmental guidelines.

Both the primary and the various secondary types are doing all they can to keep up with power-hungry portable devices, but the Zn-air technology has always had high potential when it comes to energy density. The emphasis among developers has largely been on minimizing weight, maintaining capacity and maximizing shelf life.

Most recently, Electric Fuel Corp. (Iselin, N.J.) took a step beyond Zn-air's traditional use in hearing aids and announced its "booster" throwaway series. It allows the user to plug a cell phone into its self-contained, 3-ounce power pack for three full charges. AER Energy Resources, which worked on a rechargeable Zn-air but most recently licensed its power-saving "diffusion air manager" technology to Duracell, hopes to position its battery between high-energy primaries and rechargeables for camcorders and digital cameras at a cost slightly more than alkalines. Currently, 4.5 W-hr devices for cell phones are in prototyping and may well be viable devices before the end of the year, said Dennis Sieminski, technical marketing manager.

Every few years, there's an explosion in battery activity. It's happened for most batteries, from carbon-zinc through lithium and solar. Now it's zinc-air's turn.