Batteries employing an oxygen (air) electrode, particularly those in which the oxygen electrode is combined with an alkali metal or alkaline earth metal negative electrode useful I for bulk energy storage, particularly for electric utility grid storage, as well as for electric vehicle propulsion. Batteries have an electrochemically reversible oxygen positive having a porous mixed metal oxide matrix for receiving and retaining discharge product and a dense (non-porous) separator element which conducts oxygen ions and electrons in contact with a source of oxygen.