The rate constants for the self-discharge of the cathode material nickel(III) oxyhydroxide (NiOOH) in an alkaline medium are determined using a galvanostatic titration technique. By examination of a number of common graphite materials used in battery cathodes it is found that both the type and the amount of graphite present in the electrode influence the self-discharge rate. Two competing self-discharge phenomena exist, namely, reaction of NiOOH with surface active sites on the graphite, as well as the graphite catalyzing oxygen evolution. Their respective contributions to the overall self-discharge are evaluated.