In this paper, a passive technique is examined by adding an inlet plenum to reduce the maximum temperature and improve temperature uniformity in a simple battery pack. The inlet plenum changes the direction of the flow and dramatically reduces the issues of air recirculation and dead-air regions between adjacent cells. The dimensions of the plenum and Reynolds number were optimized to enhance cooling and temperature uniformity at the cell and pack level. The results indicated that by increasing the Reynolds number to 7440, the maximum temperature decreased by 18.3% and the temperature uniformity increased 54.6%. However, there was no significant change in the maximum temperature and temperature uniformity beyond the Reynolds number of 7440. The developed battery pack achieved the desired temperature uniformity at the cell and pack level to less than 5 degrees C.