Abstract: Metal hydride batteries comprising an electrolyte composition which comprises an aqueous solution comprising one or more compounds selected from the group consisting of metal hydroxides, metal oxide/hydroxides and ammonium hydroxides where when the electrolyte composition comprises KOH, the composition also comprises a further compound selected from the group consisting of metal hydroxides, metal oxide/hydroxides and ammonium hydroxides, exhibit reduced degradation of the anode material during operation. Anode materials advantageously exhibit ?95% of the degradation of the same anode material in the same battery when replacing the electrolyte composition with 6 M aqueous KOH and exhibit conductivity of ?50% of that of 6 M aqueous KOH. Anode materials are for example ABx high capacity hydrogen storage alloys comprising Mg where x is from about 0.5 to about 5 and which has a discharge capacity of ?400 mAh/g.