NOVELTY - An air battery system includes a sealed air battery cell (10) comprising an air electrode having air electrode layer and air electrode power collector, a negative electrode having negative electrode layer and negative electrode power collector, a separator, and a sealed air battery case; and a depressurization portion (20) for reducing internal pressure of sealed air battery cell to less than atmospheric pressure.    USE - Air battery system.    ADVANTAGE - Due to the depressurization portion, the air battery system can be charged with electric power in depressurized state. Charging in depressurized state reduces the concentration of oxygen dissolved in electrolyte solution and reduces the oxygen partial pressure in sealed air battery cell, thus achieving high power charge efficiency. The air battery system prevents moisture in air from entering the air battery and achieves high power discharge efficiency.    DETAILED DESCRIPTION - An air battery system includes a sealed air battery cell (10) comprising an air electrode having an air electrode layer of conductive material, and an air electrode power collector for collecting electric power from the air electrode layer; a negative electrode having a negative electrode layer containing negative electrode active material that adsorbs and releases metal ions, and a negative electrode power collector for collecting electric power from the negative electrode layer; a separator provided between air electrode layer and negative electrode layer; and a sealed air battery case. A depressurization portion (20) reduces internal pressure of sealed air battery cell to less than atmospheric pressure. An INDEPENDENT CLAIM is included for a method of using and controlling an air battery system by reducing internal pressure of sealed air battery cell when the air battery system is charged with electric power or when the air battery system is not operating, and boosting the internal pressure of sealed air battery cell when electric power is discharged from the air battery system.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic view of an air battery system.    Sealed air battery cell (10)    Hoses (11, 21)    Electromagnetic valves (12a-12c, 22a, 40)    Depressurization gauge (13)    Depressurization pump (14)    Detectors (15, 25)    Depressurization portion (20)    Pressurization gauge (23)    Pressurization pump (24)    Pressurization portion (30)