study presented concentrates on the thermal performance of prismatic and cylindrical lithium-ion batteries at different discharge rates. Lithium-ion batteries possess the potential risk of thermal runaway while discharging in hostile conditions. The temperature rises promptly with time and high discharge rates. The scenario becomes intricate in hyper-ambient conditions. The electric vehicle drives its input energy from a lithium-ion battery pack which rests as a bed of batteries on the chassis of the vehicle. In this study, different discharge rates ranging from 1 to 5 C were considered for investigating the thermal performance of the cylindrical and prismatic lithium-ion battery. Battery performance is closely dependent on the ambient condition. In a desert-like condition where peak summer temperature rises to 50 °C, electric vehicles are difficult to operate. PCM-fin assisted structure was applied in prismatic battery and a PCM jacket was incorporated in the cylindrical battery. Both batteries were compared against a hypothetical C rate. The study reveals that a cylindrical battery stores more heat at low ambient temperature conditions when compared to a prismatic battery. Furthermore, design attributes are different for the PCM cooling system in the two lithium-ion batteries owing to the shape factor. This study attempted to cap the maximum temperature within permissible limits through the use of PCM cooling system.