Energy storage device and related management method

The device (1) has a hydrogen storage unit (7) mounted parallel to an electrochemical battery (3). The battery and the storage unit store energy provided by a generation unit (17). A measurement sensor (19) measures electric flux provided by the generation unit, and another measurement sensor (21) measures electric flux at a load (5). A control unit (23) is connected to the sensors, and controls an alkaline electrolyser (9) according to electric flux variations measured by the sensors, where control of the electrolyser is realized to partially absorb fast variations of the measured fluxes. The generation unit is a photovoltaic generator, a wind mill or a hydroelectric generator. An independent claim is also included for a method for management of an energy storage device.