A zero-dimensional model is developed for the CFx system to account for Butler-Volmer kinetics, internal cell resistance, and double-layer (or capacitive) charging. At the low rates involved, other transport processes can be neglected. Furthermore, for this system, Tafel kinetics is appropriate. This model is used to compare with discharge data for periodic pulses superposed on an otherwise low rate of discharge. The internal resistance and high double-layer capacity account for some aspects of the pulses, such as a long time relaxation when the load is changed, but do not account for other time constants of less than 1 s. For a long constant-load discharge without pulses, the model can be simplified further, with the capacitance being negligible and the internal resistance being important only at low load resistances. Development of a modified open-circuit potential function allows all discharge data for cells of different design and load resistance to be collapsed using a generalized design equation. (c) 2007 The Electrochemical Society.