In this paper we have compared nickel/metal hydride batteries made from AB(5) and Nd-only A(2)B(7) alloys with or without addition of hydrogen peroxide (H2O2). The biggest advantages Nd-only A(2)B(7) alloys have over ABs alloys are: a higher positive electrode utilization rate, lower initial internal resistance and less resistance increase after a 60 degrees C storage, and higher capacity and resistance degradation during cycling. The hydrogen peroxide was used as an oxidation agent and was added into the electrolyte before closing the cells. The H2O2 can oxidize both Co(OH)(2) in the positive electrode and MH alloy in the negative electrode. From the test results, H2O2 oxides the MH alloy preferentially over the Co(OH)(2) in the case of AB(5) alloy. This preferential oxidation is reversed in the case of the A(2)B(7) alloy in which Co(OH)(2) is oxidized first. In cells made from both alloys, the addition of H2O2 prevented the venting of cells during formation, increased the utilization of positive electrode, improved the 60 degrees C charge retention, and increased the mid-point voltage after 300 cycles. Additionally the H2O2 also improved the cell balance for A(2)B(7) alloy by decreasing the over-discharge reservoir in the negative electrode and reducing the capacity degradation in A(2)B(7) alloy. However, the addition of H2O2 in cells made with AB(5) alloy deteriorated the cell balance by increasing the over-discharge reservoir in the negative electrode. The different cell balance and failure mechanisms for the two alloy compositions and H2O2 additive were compared and discussed. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.