PURPOSE: To improve the preservation performance of a silver oxide battery, and prevent any internal short circuit which might be caused during the electric discharge by making a porous synthetic resin film, which is provided in a separator layer, has a property of inhibiting transmissions of zincate ions and argentate ions and has a mean hole diameter of within a specified range.

CONSTITUTION: A positive mixture 1 is packed into a positive can 2. A separator layer (A) consists of a translucent film 3, a cellophane film 4 and a porous resin film 5 which is formed by packing calcium hydroxide granular powder into the holes of a porous member before the above powder is bound with a synthetic resin. As an electrolyte with which a negative mixture 6 is impregnated, an aqueous causticalkali solution which is saturated with zinc oxide is used. As an electrolyte with which the positive mixture 1 and the separator (A) are impregnated, an aqueous caustic-alkali solution containing no zinc oxide is used. In a battery thus constituted, almost no capacity reduction is caused even after it is left at a temperature of 60°C and a humidity of 90% for 100 days. In addition, a stable electric resistance is realized by adjusting the mean hole diameter of the porous synthetic resin film 5, and the preservation performance of the battery rapidly decreases when the mean hole diameter of the film 5 becomes over 100μm.