To prolong the life of a battery and to enhance its excess charge resistance by using as the negative electrode a hydrogen storage alloy covered on its surface with a compound containing at least a carbonic acid, causing the compound containing the carbonic acid to contain component elements of the hydrogen storage alloy, and using the AB2 type and the like as the crystalline structure of the hydrogen storage alloy.

A hydrogen storage alloy serving as a negative electrode is covered on its surface with a compound containing at least a carbonic acid, and the compound containing the carbonic acid on the surface of the hydrogen storage alloy is a compound containing CO3, e.g. that represented by M1(CO3)x.M2(OH)y, (M1 and M2 each represent at least 1 or more of the component elements of the hydrogen storage alloy, (x) represents 0.1 to 4, and (y) 0.1 to 4). The compound is particularly effective when formed on the surface of the hydrogen storage alloy composed of elements called AB2 types, such as Zr, Ti, Ni, Mn, V, Cr, Fe, Co, and Al. Thereby the progress of reaction with oxygen gas is inhibited, and excess charge resisting characteristic and cycle life characteristic can be enhanced.