BATTERY COOLER

A battery cooler comprises a refrigerant filling chamber, a refrigerant inflow passage, and a refrigerant outflow passage. The refrigerant filling chamber is sandwiched between opposed battery unit cells and is arranged at a position for receiving heat of the unit cells. The refrigerant inflow passage is connected to a lower portion of the refrigerant filling chamber. The refrigerant outflow passage is connected to an upper portion of the refrigerant filling chamber. The refrigerant filling chamber has at least one joint part joining partially and mutually opposed wall surfaces so as to suppress expansion and deformation of these surfaces caused by the pressure of the refrigerant. An outflow side wall surface rises from a bottom surface of the refrigerant filling chamber toward a connection part of the refrigerant outflow passage. The outflow side wall surface is provided with an inclined surface directed downward from a horizontal direction.