A distinctive system within the various primary battery types is air-alkaline. The battery uses oxygen (O2) from the air as its cathode. The oxygen is led through holes in the casing to the cathode where reduction (absorption of electrons) takes place on a carbon layer. Because the battery casing only has to house an anode, the energy density per weight is on average high, between 220-300 Wh/kg (compared to 99-123 Wh/kg for a silver-oxide battery).
An additional advantage of this battery is its relatively low cost and environmentally friendly character. These batteries have an infinite storage time until they are activated by exposing them to air. After activation, the shelf life is rather short due to high self-discharge. Another disadvantage: once activated, the chemical process of energy production cannot be stopped, but it can be slowed down.
Applications of air-alkaline batteries:
Railway signal lighting
Road signal lighting
Buoyancy and signal lighting at sea
Telecommunications
Parking meters
Fencing