Mechanically alloyed Mg2Ni and a single air (oxygen) electrode are used as the anode and cathode, respectively, in a Mg2Ni|6M KOH|O2 rechargeable metal-hydride–air (MH–air) battery. The battery is tested for self-discharge by measuring the open-circuit voltage (OCV) and cycling characteristics. Battery degradation after charge–discharge cycling is characterized by means of X-ray diffraction (XRD) and scanning electron microscopic (SEM) analyses.