We report the effects in forced convection boundary condition to model the heat generated in Li-ion cell and the battery pack, using CFD technology (Computational Fluid Dynamics) in ANSYS fluent. The battery pack designs were analyzed and simulated on two different modes. One design is studied with and without insulation (superwool EST compression paper) between the cells, the other design is with and without PCM (phase change material). We look for better designs of battery pack in thermal management with phase change materials (PCMs) to the battery performance. The outcomes of this analytical model by the simulations have identified the heat dissipation. The achieved results show the comparison between the insulation and PCM that gives much more achievable satisfying thermal control, as PCM absorbs the heat and procrastinate to attain the defined maximum temperature with respect to time. The purpose of the design with PCM in battery is to limit the supply of heat, in time, to the PCM and thus extends the phase change duration and increase the heat transfer to the environment. A 0.32 mm-thick PCM is employed for the Li-ion cell, the temperature distribution becomes more uniform which is an important measure in battery thermal management.