Abstract: Disclosed herein is a battery thermal management system for maintaining the temperature of a battery pack in a hybrid vehicle below a maximum operating temperature threshold. The system comprises a battery pack having a plurality of electronically linked cells and a supply air diffuser having a pattern of openings therein for diffusing exhausted air at a substantially uniform flow throughout the battery pack. The system further comprises sensors for monitoring the temperature of at least a portion of the cells, a fan comprising an inlet through which air is drawn in and an outlet in communication with at least the supply air diffuser, for exhausting air into the first diffuser to lower the temperature of the battery pack, and an electronic control unit in communication with the sensors and the fan for controlling operation of the fan based on temperature signals received from the sensors to maintain the temperature of the battery pack below a maximum operating temperature.