Exploring efficient heat transfer working mediums is a research direction to improve the performance of liquid-cooled thermal management of power batteries. In this paper, a nanofluid-based experimental system for power battery liquid cooling is constructed, and the cooling performance of different nanofluid concentrations and inlet flow rates at different discharge rates and discharge times is investigated. The results show that the cooling performance of nanofluids at low discharge rate and low flow rate is obvious. At high flow rates, the cooling performance deteriorates severely. At high discharge rates and high temperatures, the cooling performance of nanofluids has limited improvement. High flow rate and high temperature tend to cause nanofluid failure, and the higher the concentration of nanofluid, the more obvious the effect. The optimal working conditions are 1C discharge for 60 min, 0.9 L/min flow rate, 0.1 %, 1 %, and 2 % of γ-Al2O3/heat transfer fluid nanofluid reduce the battery module by 0.24 °C, 0.31 °C, and 0.52 °C, respectively, and improve the cooling performance by 3.77 %, 5.02 %, and 8.16 %, respectively. This work is instructive for the practical application of nanofluids on battery thermal management systems.