Battery Thermal Management System plays a significant role in maintaining the health of the batteries for the long run. Active-based cooling technologies, due to the lesser thermal conductivity of air and parasitic losses, have limited applications. Passive-based cooling techniques gain importance due to their simplicity and energy efficiency. In this present work, paraffin-composite based battery modules are numerically analyzed at various extreme operating conditions. Various additives like Al2O3, carbon black, and expanded graphite (EG) were added to pure paraffin to magnify its thermal conductivity. Composite-based battery modules are numerically tested at 3C discharge rate conditions and the results are summarized. Simulations are carried out for battery modules with natural convection, Pure PCM (phase change material), and Composite PCMs. The simulation results showed that the pure PCM and CPCMs with Al2O3, carbon black, and EG reduced the temperature of battery module maximum by 2◦C, 3◦C, 2.8◦C, and 4◦C, respectively, in comparison with battery module with natural convection. The expanded graphite-based battery module was observed to reduce the maximum temperature of module maximum by 4◦C by maintaining module temperature close to 39◦C at 3C discharge conditions. In all the cases, the core of the battery modules have more heat compared to the corners and edges of the battery modules. Experimental validation was carried out by fabricating EG/PCM module and tested at 3C discharge rate conditions. Test results convey that after running for 20 min at 3C conditions, the battery module with CPCM attains the peak temperature of about 45 ◦C which is theidle operating temperature of the battery.