This paper attempt to study the effect of natural air convection of large commercial lithium-ion (Li-ion) battery prismatic cell (50Ah) for rechargeable energy storage applications of electric vehicles (EVs). In particular, a numerical thermal model was developed and experimentally validated in different ambient temperature conditions. The cell anode is graphite based, and The cathode of the cell is nickel, manganese and cobalt (NMC) based. Moreover, the surface temperature of the cell is recorded with the use of a thermal camera and thermocouples, then it was compared with simulation results.The experimental results show a rather uniform temperature distribution, with maximal temperature difference of 0.7°C, during the discharge load profile whereas the maximal temperature difference at the end of discharge load was around 1.5°C. 3D thermal modeling simulation results executed at different ambient conditions are compared and validated with the experimental results, wherein the error fluctuates around 2°C. Furthermore, the maximal temperature area was observed at the center point of the battery.Finally, the rose of the temperature in the discharge test was around 22°C at 10°C ambient condition and 20°C at 25°C ambient condition.