based on fuel-cell research allowed application to small button and prismatic primary cells for hearing aids, pagers, and medical devices, especially cardiac telemetry. Reaction formulas The chemical equations for the zinc–air cell are: Anode: Zn + 4OH- -> Zn(OH)4^2- + 2e- (E0 = －1.25 V) Fluid: Zn(OH)4^2- -> ZnO + H2O + 2OH- Cathode: 1/2 O2 + H2O + 2e- -> 2OH- (E0 = 0.34 V pH＝11) Overall 2 Zn + O2 -> 2 ZnO (E0 = 1.59 V) Zinc–air batteries cannot be used in a sealed battery holder since some air must come in; the oxygen in 1 liter of air is required for every ampere-hour of capacity used. Storage density Zinc–air batteries have higher energy density than many other types of battery because atmospheric air is one of the battery reactants, in contrast to battery types that require a material such as manganese dioxide in combination with zinc. Energy density, when measured by weight (mass) is known as specific energy. The following table shows the calculation of specific energy for a specific zinc-air battery and several other commonly available batteries of different chemistries. Storage and operating life Zinc–air cells have long shelf life if sealed to keep air out; even miniature button cells can be stored for up to 3 years at room temperature with little capacity loss if their seal is not removed. Industrial cells stored in a dry state have an indefinite storage life. The operating life of a zinc–air cell is a critical function of its interaction with its environment. The electrolyte loses water more rapidly in conditions of high temperature and low humidity. Because the potassium hydroxide electrolyte is deliquescent, in very humid conditions excess water accumulates in the cell, flooding the cathode and destroying its active properties. Potassium hydroxide also reacts with atmospheric carbon dioxide; carbonate formation eventually reduces electrolyte conductivity. Miniature cells have high self-discharge once opened to air; the cell's capacity is intended to be used within a few weeks. Discharge properties Because the cathode does not change properties during discharge, terminal voltage is quite stable until the cell approaches exhaustion. Power capacity is a function of several variables: cathode area, air availability, porosity, and the catalytic value of the cathode surface. Oxygen entry into the cell must be balanced against electrolyte water loss; cathode membranes are coated with (hydrophobic) Teflon material to limit water loss. Low humidity increases water loss;