Abstract: The improved system of the present invention comprises a plurality of electrically interconnected power modules, each module comprising a sealed pressure vessel containing a volume of hydrogen and a plurality of batteries connected in parallel and disposed in a removable rack. Each battery comprises a stack or pile of series connected metal-hydrogen cells. Means are provided for recirculating the hydrogen in the vessel around and between the cells and for cooling the hydrogen. The cooling operation for the modules may be carried out internally or externally of the vessel. A blower or the like may facilitate the recirculation of the hydrogen.The modules are series connected to supply a desired large amperage, for example to take care of peak load requirements for a commercial power generating station or the like. The system is capable of rapidly absorbing power from the station during periods of low demand and rapidly releasing the power during peak loads so as to level the load requirements.