The demand for Hybrid Electrified Vehicles (HEVs) is increasing due to government regulations on fuel economy. The battery systems in a PHEV have achieved tremendous efficiency over past few years. The system has become more delicate and complex in architecture which requires sophisticated thermal management. Primary reason behind this is to ensure effective cooling of the cells. Hence the current work has emphasized on developing a “Physics based” thermal management modeling framework for a typical battery system. In this work the thermal energy conservation has been analyzed thoroughly in order to develop necessary governing equations for the system. Since cooling is merely a complex process in HEV battery systems, the underlying mechanics has been investigated using the current model. The framework was kept generic so that it can be applied with various architectures. In this paper the process has been standardized in this context. Under this generic framework the theoretical model was extended to a Simulink model which can be integrated with existing cooling network (i.e. Flowmaster) for the PHEV system. Besides predicting coolant outlet it is also important to predict cell-level temperatures in the battery systems. The integrated model will be able to fulfill these goals. In order to establish the model’s applicability, the physics based model was correlated with vehicle level test data under different drive cycles. The results exhibited good agreement with the test data which provides significant confidence in the proposed framework and its future developments.