The characteristics of the MnO2 cathode of a MH/MnO2 battery have been studied by cyclic voltammetry, x-ray diffraction, and potentiostatic techniques. It was found that the addition of Ni(OH)(2) to the MnO2 can prevent overcharge of the MnO2 and decrease the imbalance of the charge/discharge states of the positive and negative electrodes, raise the working voltage of the MH/MnO2 cell, and prevent the formation of Mn3O4, thereby improving the rechargeability of the MnO2 electrode. The discharge mechanism is also discussed.