This paper reports a method of modeling the dependence of the discharge behavior of a lithium-ion battery (LIB) on the environmental temperature. A comparison of the experimental discharge curves for discharge rates ranging from 0.5 to 5 C and environmental temperatures of 15, 25, 35, and 45 C with the modeling results validates the two-dimensional modeling of the potential and current density distributions on the electrodes of an LIB as a function of the discharge time during galvanostatic discharge based on the finite element method. The heat generation rates as a function of the discharge time and the position on the electrodes are calculated to predict the temperature distributions of the LIB based on the modeling results of the potential and current density distributions. The temperature distributions obtained from the modeling are in good agreement with the experimental measurements.