A high voltage battery module comprises a plurality of battery cells stacked in an array. The array is covered on its ends by a pair of opposing end plates, and is covered on its sides by a pair of opposing sidewalls. The sidewalls partially cover upper surfaces of the battery cells. Internal channels provide gaps between the sides of the battery cells and the interior surfaces of the sidewalls. An external channel is vertically spaced from the internal channel and is defined by the exterior surfaces of the sidewalls. Brackets secure the end plates to the sidewalls by at least partially extending into the external channels of the sidewalls.