Phase change materials (PCMs) have found their way in heat transfer applications because of their capability to store energy during change of phase, and thermal management of lithium ion (Li-ion) batteries is not an exception. The ultimate goal of a battery thermal management system (BTMS) is to alleviate the excessive rise in temperature of cells. In the current investigation, a battery-like simulator was fabricated to simulate the heat generation in a typical Li-ion battery. Metal matrix and metal nanoparticles were added to a PCM to increase the rate of heat transfer and the results are compared to each other in order to find the best approach to manage temperature distribution around the battery simulator. According to the experimental results, it is found that the metal matrix-PCM composite decreases the maximum temperature difference between battery surface and PCM composite by up to 70%. In addition, even though all the nano-PCM composites increase the heat transfer potential of system, the composites containing Ag nanoparticles have shown better thermal performance than other composites. The results of the present study can be used as a guideline for designing battery thermal management system.