An energy storage device for an electric vehicle comprising: a housing formed by an upper wall, a lower wall and two opposing pairs of side walls (1120, 1125) defining an interior volume; a plurality of power cells, arranged in the interior volume of the housing, each power cell having a first terminal at one end and a second terminal at another end, wherein each of the plurality of power cells extending in a substantially parallel configuration with intervening spaces being provided between adjacent power cells; a resin sheet (1305, 1310) encapsulating at least one end of each of the plurality of power cells and holding the plurality of power cells in a rigid configuration; and a heat absorbing fluid within the housing, circulating through the intervening spaces contacting an exterior of at least one of the plurality of power cells, characterized in that the heat absorbing fluid enters the housing through an upper exchange port located on the upper wall and exits the housing through a lower exchange port located on the lower wall, wherein the upper exchange port and the lower exchange port, respectively, are located at diagonally opposite edges of the upper wall and lower wall, respectively, wherein said diagonally opposite edges are the shortest opposite edges of the upper wall and lower wall, respectively, and wherein the resin sheet (1305, 1310) is positioned to isolate the heat absorbing fluid from the at least one of the first terminal at the one end and the second terminal at the another end of each of the plurality of power cells and retain the heat absorbing fluid in contact with the exterior of the at least one of the plurality of power cells. a housing formed by an upper wall, a lower wall and two opposing pairs of side walls (1120, 1125) defining an interior volume; a plurality of power cells, arranged in the interior volume of the housing, each power cell having a first terminal at one end and a second terminal at another end, wherein each of the plurality of power cells extending in a substantially parallel configuration with intervening spaces being provided between adjacent power cells; a resin sheet (1305, 1310) encapsulating at least one end of each of the plurality of power cells and holding the plurality of power cells in a rigid configuration; and a heat absorbing fluid within the housing, circulating through the intervening spaces contacting an exterior of at least one of the plurality of power cells, characterized in that the heat absorbing fluid enters the housing through an upper exchange port located on the upper wall and exits the housing through a lower exchange port located on the lower wall, wherein the upper exchange port and the lower exchange port, respectively, are located at diagonally opposite edges of the upper wall and lower wall, respectively, wherein said diagonally opposite edges are the shortest opposite edges of the upper wall and lower wall, respectively, and wherein the resin sheet (1305, 1310) is positioned to isolate the heat absorbing fluid from the at least one of the first terminal at the one end and the second terminal at the another end of each of the plurality of power cells and retain the heat absorbing fluid in contact with the exterior of the at least one of the plurality of power cells.