It has been previously demonstrated that V6O13 is a very attractive cathode active material for rechargeable lithium batteries. For high material utilization it is normally expected that a carefully formulated composite cathode incorporating a suitable conductive diluent is required for acceptable electrochemical performance. In this paper the effect of conductive carbon in the positive electrode formulation is highlighted. For a composite cathode incorporating a conductive carbon, the active material in the fully discharged cathode (1.8 V versus Li/Li+) corresponds to an approximate composition of Li7.1V6O13. Without any carbon added, the composite cathode shows behavior consistent with it developing poor electronic conductivity at high lithium ion concentration (i.e. towards the end of the normal discharge curve). The fully discharged cathode in this case corresponded to an approximate composition of Li4.3V6O13. We show that the cathode polarization is the main cause for a limited discharge capacity due primarily to a minimization of the lower voltage plateau.