The use of mathematical modeling and computer simulations in the understanding of lithium/polymer battery performance is discussed. A general model of these systems is reviewed, with particular attention to the assumptions involved in the analysis. The parameters required for the model are categorized according to whether they are transport, thermodynamic, or design-adjustable properties, and the experiments necessary to measure these data are described. The role of mathematical modeling in the design process is also considered. Dimensionless groups and simple correlations useful for characterizing the primary system limitations are given. A general approach to identifying optimum values of system parameters such as electrode thicknesses is reviewed.