This study is to investigate the cooling performance of the secondary battery in electric vehicles according to three different gaps between battery cells. To accomplish the convective cooling performance of the battery surface with three different gaps, selected local positions (X, Y, Z) for various temperature distributions were marked on the gap surface contacting the cell surface. The cooling performance of the gap of 0.5 mm was compared with the gaps of 5 mm, and 1 mm. Normalized local Nusselt number of the cooling area at the normalized width position indicated that the gap of 0.5 mm was on average 26.99% lower than that of 5 mm and 0.49% lower than that of 1 mm. At the normalized height, the gap of 0.5 mm was on average 12.12% higher than that of 1 mm. Because of the vortex at the outlet area, cooling performance at the gap of 0.5 mm was on average 13.19% higher than that of 5 mm and 0.79% higher than that of 1 mm at normalized thickness. Ultimately, the best cooling performance existed at the gap of 5 mm, but the gap of 0.5 mm was best for improving space efficiency, energy storage capacity, and vehicle-driving durability.