Mechanically alloyed Mg2Ni and a single air (oxygen) electrode are used as the anode and cathode, respectively, in a Mg(2)Nil6 M KOHIO2 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. (C) 2003 Elsevier Science B.V. All rights reserved.