This experimental study investigates the thermal behavior of a 48V lithium-ion battery (LIB) pack comprising three identical modules, each containing 12 prismatic LIB cells. The objective is to investigate the thermal performance of the LIB pack under real-world operating conditions using a worldwide harmonized light duty test cycle and its inverted version. Two cases are tested whose difference is the initial state of charge (SOC), 90% for Case1 and 60% for Case2. The temperature distribution within the battery pack and cooling system is measured using 27 thermocouples. The results show that external surfaces exhibit the lowest temperatures, while the middle cells experience the highest. In addition, an abnormal temperature spike in a specific cell shows external influences or internal irregularities of the LIB cell, emphasizing the need to utilize a high number of thermocouples. Comparing Case1 and Case2, Case2 demonstrates a higher temperature rise at the cycle's beginning. The temperature gradient, the difference between maximum and minimum temperatures at each time, remains below 3.7°C for both cases. A homogeneous indirect liquid cooling system is implemented when the pack reaches 40.0°C, operating during the most thermally demanding period. However, Case2's enhanced cooling consumes more energy than Case1. Furthermore, initial SOC influences stored energy rise of the battery pack. Case2 experiences higher increases and smaller reductions compared to Case1, emphasizing the importance of initial SOC for energy balance and pack stability. This study underlines the importance of evaluating battery pack thermal behavior under real-world operating conditions, emphasizing the complexity of the LIB battery pack system, as well as the impact of a liquid cooling system on its thermal performance.
