TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Active Layer: The active layer of the air cathode may be fixed to a polymer membrane that conducts by OH- ions. The active layer of the air electrode comprises:(i) carbon carrying a dispersed oxygen reduction catalyst;(ii) 10-40 wt.% PTFE; and(iii) 10-30 wt.% of microparticles of a polymer which conducts by OH- ions.The O2 reduction catalyst is e.g. a platinoid.Preferred Method: Fixing of the electrode to the membrane is effected e.g. by hot pressing to the superficial layer of the electrode. The membrane polymer is compatible with or the same as that dispersed in the active layer of the electrode.Taking the air electrodes out of the circuit during charging sequences is accomplished by external switching of the electrodes, this being effected only after the main circuit has been broken.Preferred Components: The compartment housing the auxiliary positive electrodes is separated from the zinc electrodes by a polymeric ion exchange membrane with OH- ion conduction which limits the passage of zincate ions and dendrites of metallic zinc. The membrane is e.g. a microporous membrane in which the microporosity is due to a mineral oxide or hydroxide filler. EXAMPLE - A 50 Ah air Zn cell was made with two Zn electrodes (Q) 145 x 145 mm, two air electrodes (J) and two auxiliary positive electrodes (G). The 5 compartments of the cell (2 x A, 2 x B and C) were sealed together by membrane gaskets (D, H) compressed by bolts (E). The chambers (F) holding the auxiliary electrodes were filled with 3.5-4.5 M KOH as electrolyte. The auxiliary electrodes (G) were of perforated Ni foil. The Zn electrodes (Q) were made by applying a paste containing (by wt.) 82% ZnO, 12% Ca(OH2), 2% CdO and 4% PTFE to a cadmium coated perforated Cu foil. The air electrodes (J) were sealed to the membranes (D) and comprised a carbon fabric coated with a mixture of carbon black and PTFE. The superficial layer of the electrode in contact with the membrane was comprised of a mixture of carbon black bearing Pt as oxygen reduction catalyst, PTFE and microparticles of a polymer with OH- ion conductivity.    The electrode was hot pressed to the membrane. The membranes used was of Neosepta AMH (RTM). The membranes (H) separating the Zn electrodes from the auxiliary electrodes were of an ion exchange membrane e.g. of microporous polyethylene filled with SiO2 and impregnated e.g. with a mineral hydroxide such as Ni(OH)2. Separators (I) e.g. of fibrous polyamide are preferably provided between the membranes (H) and the Zn electrodes. A corrugated current collector (K) e.g. of Ni coated perforated Cu foil was provided between the two air electrodes.    The cell was charged using the auxiliary electrodes with the zinc electrodes disconnected. The cell was charged and then discharged at 25 A for 2 hours at an average voltage of 1.10 V. Under these conditions the discharge characteristics remained stable over 500 charge and discharge cycles.