Embodiments of the present disclosure include an apparatus for enclosing energy storage devices. An apparatus according to the present disclosure can include: an elongated sleeve having a contoured interior configured to enclose each of a plurality of energy storage devices, wherein the elongated sleeve is composed at least partially of a thermally conductive material; and at least one slot disposed on an exterior surface of the elongated sleeve, wherein the at least one slot is configured to receive for mechanically coupling a mounting rail to the elongated sleeve.