A battery pack (10; 110) for a power tool includes a housing (18) made of a rigid material. The housing contains a cooling air passage (54), which is in gaseous communication with the outside environment, and at least one isolated space (52). At least one isolating wall (44) is disposed inside the housing so as to physically separate and isolate the cooling air passage from the at least one isolated space. A plurality of battery cells (32) is disposed within the housing such that an end portion (32a) thereof is disposed within the at least one isolated space and an intermediate portion (32b) thereof is disposed adjacent the cooling air passage. First portions (78) of the at least one isolating wall respectively contact the plurality of battery cells and are comprised of a material that is more flexible and/or elastic than the rigid material of the housing (18).