In this paper, a novel design including cooling media for packing the rechargeable Lithium (Li)-ion batteries used in hybrid and electric vehicles is proposed. The proposed battery pack satisfies all thermal and physical issues relating to the battery packs used in vehicles such as operating temperature range and volume, and furthermore it increases the battery life cycle and charge and discharge performances. The temperature and voltage distributions of the proposed battery pack are calculated using the characteristics of a sample Li-ion battery and heat transfer principles. The proposed battery pack uses several distributed thin ducts for cooling which is based on distributed natural convection. Ultra uniform voltage and temperature distributions, minimum temperature dispersion in each battery unit, minimum increase in the battery pack volume, natural convection (no extra energy consumption for cooling), the maximum observed temperature less than that in other proposed battery packs and high thermal performance for different ambient temperatures until 48 °C are some advantages of the proposed Li-ion battery pack including proposed distributed cooling media. Simulation results and a comparison between the parameters of the proposed cooling media and other related work are presented to validate the theoretical results and to prove the superiority of the proposed battery pack design.