Hybrid vehicles utilize a high voltage battery pack to improve fuel economy by maximizing the capture of vehicle kinetic energy for reuse. Consequently, these batteries experience frequent and rapid charge-discharge cycles. The heat generated during these cycles must be managed effectively to maintain battery cell performance as well as pack life. The battery cooling system must keep the pack temperature below a design target and approximately uniform across all cells in the pack. Here, the authors discuss some of the design points of the air cooled battery packs in Ford’s current model Fusion and C-Max hybrids. In these vehicles, flow of battery cooling air was required to not only provide effective cooling of the battery cells, but to simultaneously cool a DC-to-DC (high to low DC voltage) converter module. In addition to the fundamental heat transfer goals, the design team was challenged to satisfy constraints associated with package and air “rush” noise (battery cooling fan NVH); among others. The efforts to meet the, often competing, design requirements using a variety of test and analytical methods are discussed.