A pack level passive thermal management system has been designed, developed and experimentally investigated using a phase change composite material. Three 20Ah capacity LiFePO4 prismatic cells connected in series are used to form the battery pack and phase change composite material of different thicknesses are tested. The battery pack has been charged at 1C and discharged at 1C, 2C, 3C and 4C. A total of 18 thermocouples are used to measure the temperature at the principal surface of all three cells. The results obtained with the phase change composite material are compared with no cooling and liquid cooling options. The results show that, with the use of 6mm thick phase change composite material plates, the battery surface temperature reduces from 56.5°C at no cooling to 36.5°C at a 4C discharge rate. Even at a 1C discharge rate, the temperature of the battery pack drops from 33.5°C with no cooling to 29.1°C with phase change material plates. It is also observed that the effect of an increase in phase change material thickness on the battery pack temperature is insignificant beyond a 6mm thick plate. The results show that the temperature gradient is significantly lower with phase change composite material compared to no cooling and liquid cooling.