This study contains a systematic investigation of RT-44 and GNP/RT-44 composite performance in passive thermal management of a battery pack operating at different climate temperatures. The thermal characterization of RT-44 and GNP/RT-44 composites was also carried out. For 7% GNP/RT-44 composite, solid phase and liquid phase thermal conductivities were enhanced by 230% and 130%, respectively. On the other hand, loss of energy storage capacity is about 7.5% compared to RT-44. During the passive thermal management, the temperature increase of battery was significantly reduced by RT-44 due to their sensible and latent energy storage capability. This superior performance is further enhanced by the increased thermal conductivity of 7% GNP/RT-44 composites. At the highest discharge rate (3.90 W) and at the highest ambient temperature (30 degrees C), the effective thermal protection duration was extended as 1.96 and 7.90 times compared to RT-44 and natural convection cases. Moreover, it is further extended by the reduction both the discharge rate and ambient temperatures. 7% GNP/RT-44 also reduced the maximum temperature difference within the battery pack at low ambient temperatures. On the other hand, RT-44 performed better maximum temperature difference at higher ambient temperatures due to phase change and constant temperature plateau effect.