New energy vehicles are mainly powered by high energy density batteries that can experience thermal safety issues that have received extensive attention from researchers. The battery thermal management system is designed to prevent thermal runaway in the batteries. This paper presents a coupled heat transfer and battery heat generation study using porous medium composite phase change materials (CPCM) for battery thermal management. The study uses numerical models and experiments with particle image velocimetry (PIV) to research the heat generation in lithium-ion batteries in the porous composite phase change unit and the heat transfer in the composite phase change materials. The results show that the porous media accelerate melting of the phase change materials (PCM), composite phase change materials can slow the battery temperature increase and the current intensity can significantly impact the melting process, energy storage and energy storage efficiency of the thermal management system. Thus, the composite phase change material improves the heat dissipation in the battery which slows the temperature increase. Dual-battery models should have a space between the batteries to improve the heat dissipation for the thermal management system.