The characteristics of lithium cells with MnO2, and (CF), cathodes were investigated for two different electrolyte compositions, i.e., LiClO4/PC + DME and LiClO4/PC. For such lithium cells, the greater loss of long-term storage capacity was found in the case of cells using mixed PC + DME electrolyte. The oxidation process of DME by the cathode elements during the storage period is assumed to be the cause of the capacity loss. In the case of cells using MnO2, as a cathode, the polymerisation process of the oxidation products of DME on the cathode surface can be also considered. After storage at 45 degrees C, the smaller loss of capacity was found for the cells using MnO2, as a cathode. The different behaviour of these two kinds of cells during a pulse discharge was also confirmed.