Cooling air intake port (52), cooling air exhaust port (55), and securing walls (86, 87), which contact and secure the side surfaces of one or more battery cells (72), may be defined within two battery pack housing halves (50, 80). When battery pack (99) is assembled, at least one cooling air passage (91, 92) is defined by the side surfaces of the battery cells, the interior surface of the battery pack housing, and the securing walls. The cooling air passage connects the cooling air intake port to the cooling air exhaust port. Further, the securing walls isolate or physically separate the cooling air passage from battery terminals (72a, 72b). By forcing cooling air through the cooling air passage, the battery cells can be effectively and efficiently cooled. In addition, if the battery terminals are isolated from the cooling air by the securing walls, the electrical contact areas of the battery cells are protected or shielded against outside moisture and foreign substances that may be introduced into the battery pack by the cooling air.