A method for treating three-dimensional current and temperature distributions in large-scale battery modules is described. Simulations are presented for a module consisting of cells formed with a lithium metal anode, a polymer electrolyte, and a vanadium oxide cathode. The calculations illustrate the nonlinear dependence of power output on system temperature, which for the investigated lithium-polymer battery module is determined primarily by the influence of temperature on the electrochemical reaction rates and ionic conductivity. An appendix is devoted to the estimation of physiochemical parameters, some of which are not available from the current literature, bur are nonetheless important model inputs.