NOVELTY - The system (10) has a battery (14) i.e. cold battery pack, discharging thermal energy. A housing (16) includes a chamber (24) to receive the battery, and contains saturated liquid coolant (26) that immerses a heat sink (20) such that the coolant receives thermal energy from operation of the battery to cause phase change of the coolant from a liquid phase to a vapor phase. A heat exchanger (18) receives vapor phase coolant from the chamber, removes thermal energy from the vapor phase coolant, and returns the liquid phase coolant to the chamber.    USE - Battery temperature control system for use in a vehicle e.g. hybrid electric vehicle (HEV) and full electric vehicle.    ADVANTAGE - The system utilizes the heat exchanger and a cooling fan to manage heat transfer from the vapor phase coolant to the environment external of the system, thus maintaining target pressure and corresponding target temperature of the coolant and providing a stable temperature environment for battery cell heat sink structure. The system is inherently isothermal, and does not require forced fluid flow within the battery to perform required heat exchange functions, thus allowing natural flow of high energy vapor phase coolant to the heat exchanger instead of requiring a pump to force flow of coolant to the heat exchanger. The system allows circulation of saturated fluids such as liquid-vapor refrigerant, to transport thermal energy from the battery to the heat exchanger, so that the liquid phase coolant can be exposed to the heat exchanger along with the vapor phase coolant and the thermal energy from a portion of the liquid and the vapor can be transferred by the heat exchanger to an external environment, thus cooling the vapor and the portion of the liquid and facilitating improved heat transfer in the system, and hence avoiding use of a pumping mechanism.    DETAILED DESCRIPTION - The saturated liquid coolant is 1,1,1,2-Tetrafluoroethane or 2,3,3,3-tetrafluoroproplene. An INDEPENDENT CLAIM is also included for a vehicle battery temperature control method.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of a battery temperature control system employed in a vehicle.    Vehicle battery temperature control system (10)    Battery (14)    Housing (16)    Heat exchanger (18)    Heat sink (20)    Chamber (24)    Saturated liquid coolant (26)