Nickel metal hydride storage battery with a safety valve for relieving excess gas pressure in the battery when the safety valve is open, the safety valve having a hydrogen-permeable valve member for allowing hydrogen-gas leakage therethrough when the safety valve is closed

Abstract

A nickel-metal hydride storage battery is provided capable of suppressing changes in discharge reserve and charge reserve of a negative electrode to prevent lowering of battery characteristics for a long term. A nickel-metal hydride storage batteryof the present invention comprises a battery main part (an electrode plate group, an electrolyte, and others), a casehousing this battery main part, and a safety valve device. The safety valve deviceincludes a valve memberof a closed-end substantially cylindrical shape. This nickel-metal hydride storage batteryis arranged such that a hydrogen leak rate V(μl/h/Ah) of the battery having been charged and discharged and then charged to 60% SOC satisfies a relationship: 2≦V≦4, the hydrogen leak rate being per unit of battery capacity under an atmosphere at a battery temperature of 45° C., and a reduced pressure of 10 kPa.