This paper presents a circuit model for a 100 Ah Lithium Polymer Battery that takes into account the effect of temperature and discharge rates. This is done by studying the behavior of two advanced 100 Ah Lithium Polymer Battery cells under different load condition and at different temperatures, to extract the RC parameters needed to develop the equivalent circuit model. This paper presents a methodology to identify the several parameters of the model. The parameters of the circuit model depend on both, battery cell temperature and discharging current rate. The model is validated by comparing simulation results with experimental data collected through battery cell tests. The simulation results of the battery cell model are obtained using MATLAB, and the experimental data are collected through the battery test system at battery evaluation lab at University of Massachusetts Lowell. This model is useful for optimization of the battery management system which is needed to run a battery bank safely in an electric car.