A battery pack includes a plurality of cell assemblies each of which include one or more prismatic batteries. A frame has legs sized and configured to be positioned around the prismatic batteries. At least one leg includes a rear face, curved outer edge and a side face. A thermal transfer sheet is made from a sheet of a compressed mass of exfoliated graphite particles. Each thermal transfer sheet is positioned to contact the major surface of the at least one prismatic battery and is bent over the curved outer edge. At least a portion of each thermal transfer sheet is secured between a heat sink and the side face.