A battery pack includes a housing and electrochemical cells disposed in the housing. The housing includes a container and a lid that closes an open end of the container. The container has a base, an outer wall the surrounds the base, and a first and a second inner wall disposed inside the outer wall. The first inner wall extends between, and is fixed to, a first portion and a third portion of theouter wall, and is spaced apart from a second portion and a fourth portion of the outer wall. The second inner wall extends between the first portion and the third portion, and is disposed between thefirst inner wall and the fourth portion. The second inner wall is movable relative to the outer wall such that spacing of the second inner wall from the first inner wall can be changed.