Lithium ion (Li-ion) batteries are promising power sources for hybrid propulsion systems, and thermal management of batteries has been identified as a critical issues for their safe and efficient application. This work studied thermal management of Li-ion battery pack both experimentally and computationally. A battery pack consisting of multiple cells was fabricated and experimentally tested in a wind tunnel facility. Systematic tests were performed under various flow velocity, charging and discharging current, and pack configuration. Computationally, a high-fidelity two dimensional CFD-FEA (Computational Fluid Dynamics and Finite Element Analysis) model was developed to capture the detailed dynamics of thermal management of the cells. Temperature rise of cells and pressure measurements were recorded in the experiments, and compared with model simulations. Reasonable agreement was obtained, confirming the validity of the model and also revealing possible directions for future work.