The oxygen evolution and recombination kinetics in Ni-based battery systems have been investigated under temperature-controlled, steady-state, overcharging conditions within a temperature range of 0-60 degrees C. Theoretical relationships for both reactions have been derived. The mathematical relationships have been confirmed by experiments on sealed rechargeable NiCd batteries. Under steady-state overcharging conditions, the Cd electrode potential was proven to be constant, thereby significantly reducing the complexity of the interpretation of the results. The oxygen evolution reaction was found to be a two-step process at the Ni electrode: two linear Tafel dependencies were found at low and high currents, separated by a transition region at intermediate currents. The oxygen recombination kinetics was found to be first-order in partial oxygen pressure, strongly suggesting that the recombination reaction is purely diffusion-controlled by oxygen, redissolved into the electrolyte, to the Cd electrode surface. For all reactions, activation energies have been determined. The results can directly be applied to aqueous battery models and give more insight into both the overcharging and self-discharge processes occurring in these Ni-based systems. (c) 2005 The Electrochemical Society. All rights reserved.