The Li-CFx system has been successfully used in implantable batteries to power medical devices for humans. Amassed data is analyzed to show that the behavior is dominated by the open-circuit potential and Tafel kinetics. Data from several discharge load resistances can be collapsed onto a single curve on this basis. At the low rates of interest, transport limitations can be neglected. Data for open-circuit relaxation show that the potential is a straight line when plotted against the logarithm of time. This is in harmony with the dominance of Tafel kinetics. (c) 2007 The Electrochemical Society.