NOVELTY - A cooling system (100) comprises cooling loop in heat transfer communication with battery (110), for removing heat with a coolant (114); first cooling device which uses a refrigerant fluid to transfer heat with the coolant; second cooling device which uses ambient air to transfer heat with the coolant; temperature determining components for determining ambient temperature and battery temperature; valve for directing the coolant to a selected cooling device; and controller (160).    USE - Cooling system for vehicle battery (claimed).    ADVANTAGE - The system is capable of retaining the performance of battery while removing heat to prevent damage due to overheating and to prevent a possible fire hazard to a vehicle. It makes possible for a high voltage battery to be cooled with a coolant flowing at a high flow rate to ensure homogeneous cooling of all cells (108) in a battery pack.    DETAILED DESCRIPTION - Cooling system (100) comprises cooling loop in heat transfer communication with battery (110), for removing heat with a coolant (114); first cooling device selectively coupleable to the cooling loop, using a refrigerant fluid to transfer heat with the coolant; second cooling device selectively coupleable to the cooling loop, using ambient air to transfer heat with the coolant; temperature determining components for determining ambient temperature and battery temperature; valve for directing the coolant to a selected cooling device to limit a temperature gradient between the coolant and battery; and controller (160) for implementing a coolant flow bypass function by commanding operation of the valve to bypass the selected cooling device in response to the battery temperature and/or ambient temperature. An INDEPENDENT CLAIM is included for a method of cooling a vehicle battery.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic view of a battery cooling system.    Cooling system (100)    Cell (108)    Battery (110)    Coolant (114)    Duo valve (150)    Controller (160)