A lead battery comprising as an active material a formation product of a novel lead monoxide or a heat treatment product thereof is disclosed. This novel lead monoxide has a true density of 8.3 to 9.2 g/cc, an average particle size not larger than 0.2.mu., an infrared absorption peak at a wave number of 1400 to 1410 cm.sup.-1 and a chromic anhydride reactivity of at least 94%.This lead battery is excellent over lead batterys comprising active materials formed from known starting substances with respect to the active material utilization ratio and it has a very long life and stable capacities. In this lead battery, the active material utilization ratio can be maintained at a very high level over a long period.