Air-cooled battery thermal management system (BTMS) technology is commonly used to control the temperature distribution of the battery pack in an electric vehicle. In this study, parallel plates are introduced to improve the cooling efficiency of the BTMS, which can change the airflow distribution of the battery pack. Firstly, the effect of the number of parallel plates on the cooling performance of the BTMS is investigated; within the acceptable range of power consumption loss, the model with two parallel plates shows the best cooling efficiency, and Tmax and ΔTmax are reduced by 2.42 and 3.46 K, respectively. Then, the influences of the length and height of parallel plates are studied; the optimal values for length and height are 1.5 and 30 mm, respectively. Finally, the conclusions drawn above are used to design three optimization schemes for the model with four parallel plates; the cooling efficiency of the battery pack can be improved efficiently, which illustrates the feasibility of the above conclusions. Compared to the original model, Tmax and ΔTmax are, respectively, reduced by 3.37 K (6.17%) and 5.5 K (71.9%) after optimization.