In this study, a coupled battery model was developed by employing a novel entropic term estimation procedure to predict the thermal behavior of a Li-ion battery for varying charge and discharge rates under different operating temperatures. In the experimental part, a battery testing system was first used to determine the fundamental thermal and electrical operational behavior of a Li-ion battery at various galvanostatic charge and discharge rates. Besides, battery tests for two different driving cycle loads based on a prototype electrical vehicle model have been conducted to simulate dynamic conditions. The first set of experiments consists of three different galvanostatic charge and discharge rates (0.5C, 1.0C and 1.5C) for three different ambient temperatures and it is used to predict the reversible heat generation term in the model. It is shown that the difference between the model and experimental temperatures are less than 2 degrees C for all galvanostatic charge and discharge rates at different ambient conditions. In the case of dynamic conditions, the maximum temperature difference between the measured and predicted values is found to be less than 2.5 degrees C for the tested highway-FTP driving cycle and less than 1 degrees C for the tested CITY-I USA driving cycle at two different ambient temperatures. In summary, the predictions of the developed model that includes a novel entropic term estimation procedure are found to be accurate enough to simulate the transient thermal characteristics of the battery cell under dynamic conditions.