The invention discloses a device and a method for retaining battery cells of traction batteries. A vehicle traction battery cell retainer includes a sidewall defining a plurality of windows each surrounded by a window flange extending therefrom, a top channel extending from the sidewall and terminating in a top flange, and a bottom channel extending from the retainer sidewall, defining a plurality of air bypass windows, and terminating in a bottom flange, the top and bottom flanges arranged for interlocking with an adjacent retainer of the traction battery. A vehicle traction battery assembly includes first and second adjacent battery cell arrays each having associated first and second retainers having a sidewall defining air flow windows and integrated top and bottom channels formed of unitary construction with interlocking flanges to couple the first and second arrays.