The present work is aimed at developing a simplified model for investigating numerically a Li-Ion battery pack storage with phase change material (PCM). The developed model is based on the energy balances for the battery cells and the PCM with a heat generation source. To simulate the phase transition phenomena in the PCM, the PCM specific heat capacity is expressed as a temperature-dependent function. The verification of the proposed model is carried out by comparing the numerical results with the experimental data from the literature and the maximum relative error obtained is approximately 6%. With the help of the validated model, the battery pack is explored during both charge and discharge cycles and the effect of various design and operating parameters on the battery temperature is reported and discussed. Results show that the use of PCM in the battery pack is appropriate and reduces the maximum battery temperature by up to 3 • C compared to a battery pack without PCM. Improving the airflow around the storage system can significantly increase the thermal management performance of the PCM and reduce the maximum temperature of the batteries by up to 2.5 • C. It has been also shown that PCM A-32 H is suitable for the battery pack than PCMs RT-31, RT-35 HC and A-36 due to its transition temperature and to its high latent heat of fusion. Eventually, the fast and simplified thermal model can be employed by battery pack designers to explore and optimize the thermal management system of the PCM with reasonable accuracy.