A battery module includes a top cover and a bottom cover affixed together to accommodate a battery set, which has a conducting terminal device exposed out of the bottom cover for the connection of an external electronic device, and a movable member supported on the top surface of the bottom cover and held in a first position by spring members to block the through holes of the bottom cover and movable from the first position to a second position to open the through holes of the bottom cover for ventilation to dissipate heat when the battery module is connected to an external electronic device.