4.2.6 Zinc-air cell Looks similar to mercury cell but have about twice the capacity. It uses air in its chemical sequences, and are usually supplied sealed; pulling a tab off energizes the cell by letting air in. Zinc-air cell Merits It has a very long storage or shelf life before being de-energized, It has a high e.m.f. of about 1.4 volts, and It is relatively cheap.