Prototypes of fuel cells based on zinc/air chemistry have been developed for use as, among other things, 2.5-kW backup power sources in rack-mounted configurations. Recent improvements made to the 75-year-old technology, such as development of more efficient cathode, fueling and multi-cell designs, are helping pave the way for the cells to challenge batteries in a number of applications. The recyclable fuel cells are based on highly plentiful materials (zinc and oxygen) and are said to be environmentally safe, produce zero emissions, charge in just minutes or seconds, and remain maintenance-free for up to 10 years. To generate electricity, zinc pellets are combined in a cell with the oxygen in ordinary air in the presence of an electrolyte to form zinc oxide. The chemistry is reversed by using electricity, with the oxygen released back into the atmosphere, leaving pure zinc pellets in the electrolyte to be used as fuel again. The 2-kW zinc/air fuel cells use a voltage controller to regulate output voltages and employ an auxiliary power source in a charged state to provide initial ride-through and peak power to handle momentary in-rush currents. Other features include standard output voltages of 12 Vdc and 120 Vac, run-time at 1/2 load of two hours, overall efficiency (round-trip charge/discharge cycle) of 50% to 60%, and an operating temperature range of 32¡F to 104¡F. Size is about 13" x 15" x 15". For more details, contact Jeffrey Colborn at METALLIC POWER, Carlsbad, CA. (760) 476-8000.