The rate of self-discharge in lithium half-cells with the spinel-type LiMn2O4 cathode was investigated in the 60–75°C temperature range. The time dependence of the capacity loss and the open-circuit voltage (OCV) was monitored during the thermal aging. Lithium re-intercalation from the electrolyte appears to govern the mechanism of self-discharge in the two plateaus at the ‘4V’ areas. Treatment of the OCV data acquired during aging and by the Galvanostatic Intermittent Titration Technique (GITT) method allowed the electrode composition to be determined during the course of self-discharge. Self-discharge current was then determined and plotted against OCV. The isothermal voltammograms obtained show characteristic self-discharge current peaks.