The authors develop two-dimensional and three-dimensional simulation codes of the transient response of the temperature distribution in the lithium ion secondary battery during a discharge cycle. At first, a two-dimensional simulation code for a cylindrical battery is developed, and the simulation results for a commercially available small size battery are compared with the corresponding experimental results. The simulation results of the transient temperature and voltage variations coincide very well with the experimental results. The simulation result of the temperature difference between the center of the battery body and the center of the battery side is also in reasonable agreement with the experimental result. Next, the authors develop a three-dimensional simulation code and perform numerical simulations for three large size prismatic batteries with the same capacity and different cross sectional shapes. It is made clear that selecting the battery with the laminated cross section has a remarkable effect on the suppression of the temperature rise in comparison with the battery with square cross section, whereas the effect of the lamination on the suppression of the temperature unevenness is unexpectedly small. These results indicate the accuracy and usefulness of the developed simulation codes. (c) 2007 Elsevier Ltd. All rights reserved.