Currently, many electric vehicles are adopting batteries with higher energy density or serial/parallel combination of many batteries for longer mileage. However, significant heat is generated in these batteries, deteriorating performance, life, and stability. In this context, an appropriate battery thermal management system is essential. An indirect liquid cooling method using the cooling plate is widely used among various battery cooling methods, however, there is a limitation on improving the performance with straight channel design. In this paper, newly proposed cooling plate design with diverging channels and oblique fins are investigated for the battery thermal management compared with a conventional straight channel design. A dynamic volumetric heat generation was calculated with battery discharge experiment with a 94Ah prismatic battery module. The straight and diverging cooling plate with oblique fins were made and used for the battery cooling experiment and the battery cooling simulation model was validated with these results. With this validated model, the effects of the cooling plate design were compared with several temperature indicators and analyzed the theoretical effect by using the heat transfer coefficient. Finally, the battery cooling simulation was conducted on the battery pack-level which is applied in real electric vehicles. The maximum temperature and temperature deviation were reduced by 3.7% and 19.1%, respectively. In addition, a pumping power can be reduced by 67.8% to satisfy 35°C of the maximum temperature and 5°C of the temperature difference of the battery pack.