Lead acid batteries are still widely used for SLI (Starting–Lighting–Ignition) systems in vehicles because of the cost advantage. The batteries are frequently charged and discharged under different operation conditions, which continuously changes distribution of inner temperature of batteries. Variation of the temperature distributions significantly affects performance and durability of the battery. We developed a one-dimensional dynamic model based on the first principle of thermal dynamics and electrochemistry. The thermal model incorporates control volumes for each of the major constituents of the battery cells that is casing, electrolyte, and electrodes. The model was extended for a six-cell battery and used to analyze effects of discharging currents on the performances and temperature, compared with results from a three-dimensional finite element analysis and tested against experimental results obtained from a thermal chamber and using thermal imaging.