A battery pack comprising a battery pack housing including a first side, and a third side that is parallel and opposed to the first side, an inner surface of the first side facing and being spaced apart from an inner surface of the third side; a second side adjoining the first side and a fourth side opposed to the second side. a first rail that protrudes from the inner surface of the first side, the first rail including a first surface feature, a second rail that protrudes from the inner surface of the third side, the second rail including a second surface feature, a battery module disposed in the battery pack housing so as to reside between the first side and the third side, the battery module including a module housing, an outer surface of the module housing including a third surface feature and a fourth surface feature, and electrochemical cells disposed within the module housing, wherein the first surface feature and the second surface feature comprise one of a protrusion and a slot, the third surface feature and the fourth surface feature comprise the other of the protrusion and the slot, and the slot is shaped and dimensioned to receive and support the protrusion, the protrusion is disposed in the slot, and the module housing is located and retained relative to the battery pack housing via engagement of the first surface feature with the third surface feature, and engagement of the second surface feature with the fourth surface feature, wherein the first surface feature and the second surface feature are aligned in a direction perpendicular to the inner surface of the first side, wherein the battery pack housing first side includes plural parallel and spaced apart first rails, each first rail including a first surface feature, and the battery pack housing third side includes plural second rails, each second rail aligned with one of said first rails, characterized in that the first slot includes a seat portion and a chamfered guide portion that is disposed between the seat portion and the first support surface. a battery pack housing including a first side, and a third side that is parallel and opposed to the first side, an inner surface of the first side facing and being spaced apart from an inner surface of the third side; a second side adjoining the first side and a fourth side opposed to the second side. a first rail that protrudes from the inner surface of the first side, the first rail including a first surface feature, a second rail that protrudes from the inner surface of the third side, the second rail including a second surface feature, a battery module disposed in the battery pack housing so as to reside between the first side and the third side, the battery module including a module housing, an outer surface of the module housing including a third surface feature and a fourth surface feature, and electrochemical cells disposed within the module housing, wherein a module housing, an outer surface of the module housing including a third surface feature and a fourth surface feature, and electrochemical cells disposed within the module housing, wherein the first surface feature and the second surface feature comprise one of a protrusion and a slot, the third surface feature and the fourth surface feature comprise the other of the protrusion and the slot, and the slot is shaped and dimensioned to receive and support the protrusion, the protrusion is disposed in the slot, and the module housing is located and retained relative to the battery pack housing via engagement of the first surface feature with the third surface feature, and engagement of the second surface feature with the fourth surface feature, wherein the first surface feature and the second surface feature are aligned in a direction perpendicular to the inner surface of the first side, wherein the battery pack housing first side includes plural parallel and spaced apart first rails, each first rail including a first surface feature, and the battery pack housing third side includes plural second rails, each second rail aligned with one of said first rails, characterized in that the first slot includes a seat portion and a chamfered guide portion that is disposed between the seat portion and the first support surface.