NOVELTY - The exchanger (2) has self-regulating and positive temperature coefficient heating elements (6) located in surface of multiple coolant conduits (4) for transferring heat to coolant fluid parts (5). Multiple fin elements (8) are located in another surface of the coolant conduits to perform a heat transfer process between air stream parts (9) and the coolant fluid parts. Headers (12, 14) are connected with the coolant conduits, and a fluid tight seal i.e. header gasket, is provided in sides of the headers. Side channels (20, 22) are provided between the headers.    USE - Integrated charge air heat exchanger for a proton exchange membrane fuel such as hydrogen and oxygen, cell stack such as power source and electrochemical device, of a fuel cell system (claimed), in an internal-combustion engine of an electric vehicle.    ADVANTAGE - The exchanger efficiently minimizes manufacturing complexity of the fuel cell system, reduces cost of the fuel cell system and combines coolant heater and charge air cooler functions easily into a single unit. The exchanger maintains the temperature of the fuel cell stack within the temperature range under normal operation. The coolant conduits of the heat exchanger unit maximize a contact area with the heating elements. The exchanger supplies the electrical power to the heating elements for heating the coolant fluid during start-up operation of the fuel cell stack under cold ambient conditions. The exchanger avoids overheating of the coolant fluid, and includes a support part for preventing undesirable deflection of the coolant conduits, when the fuel cell stack is placed under compression. The exchanger avoids undesirable dehumidification and degradation of the membranes of the fuel cell stack. The exchanger combines the heating elements and the fin elements in a single unit to reduce a packaging space in an interior part of the vehicle.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a fuel cell system comprising a fuel cell stack    (2) a method for regulating temperature of a fuel cell stack.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of an integrated charge air heat exchanger.    Integrated charge air heat exchanger (2)    Coolant conduits (4)    Coolant fluid parts (5)    Self-regulating and positive temperature coefficient heating elements (6)    Fin elements (8)    Air stream parts (9)    Headers (12, 14)    Side channels (20, 22)