Patent ID: 7758994

Claim:
A nickel-metal hydride storage battery comprising: a battery main part; and a case which houses the battery main part and forms a gas release hole through which gas in the case can be released from the case; and a safety valve device including further comprising: a valve member having a sealing surface, a flange, a top wall, and a cylindrical peripheral wall, the flange extending radially outward from a bottom portion of the cylindrical peripheral wall, the top wall and the cylindrical peripheral wall defining a space in-between the top wall and the case, and the valve member having a closed position wherein the sealing surface contacts a portion of the case around the gas release hole to close the hole, and an open position wherein when an inner pressure in the case exceeds a predetermined value, the sealing surface of the valve member separates from the portion around the hole to release gas from the case; and a valve cap having an outer peripheral wall and covering the valve member, and an aperture in the valve cap; wherein the valve member is made of a hydrogen gas permeable rubber, allowing hydrogen gas in the case to permeate through the valve member and leak out of the battery at a hydrogen leak rate V 1 (μl/h/Ah) per unit of battery capacity when the sealing surface is in the closed position, and wherein the hydrogen leak rate V 1 (μl/h/Ah) of the battery, which has been subjected to charging and discharging and then charged to 60% SOC, satisfies a relationship: 2≦V 1 ≦14 under an atmosphere at a battery temperature of 45° C. and a reduced pressure of 10 kPa.