Effective thermal management of high power density batteries is essential for battery performance, life, and safety. This paper experimentally investigates direct mineral oil jet impingement cooling of the lithium-ion (Li-ion) battery pack. For the first time, experimental results of mineral oil-based cooling of batteries are reported. Both charging and discharging characteristics on temperature uniformity and of a Li-ion pack are considered. Temperature uniformity among cells, as well as within individual cells, is experimentally measured. As a baseline, cooling of the battery pack by free-convective airflow is also reported. Two different jetting configurations: (a) submerged jet and (b) direct-jet impingement are considered. For the highest charge-discharge rates considered (2C charge and 3C discharge), mineral oil nearly maintains uniform skin temperature among the cells (less than 1 °C) as well as within the cell. Based on the results obtained, modular jet oil cooling is an excellent cooling solution of lithium-ion packs applicable to stationary electrical storage and transportation applications.