NOVELTY - A battery pack (20) comprises: a set of battery modules (22, 24) mounted within a casing; and a heat exchanger for receiving a fluid, and at least one fan, the heat exchanger and the fan being at an intermediate position between groups of battery modules that make up the set of battery modules, and a valve to selectively connect one of two sources of fluid to the heat exchanger (100), one of the two sources being at a higher temperature for providing heating fluid to the heat exchanger, and a second of the sources being at a lower temperature to provide cooling fluid to the heat exchanger.    USE - The battery pack and electronic driveline are useful for a vehicle (claimed).    ADVANTAGE - The battery pack is highly reliable and efficient.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are:    (1) an electronic driveline for a vehicle comprising: at least one electric motor, the electric motor thawing power from a battery pack; and a heat exchanger for receiving a fluid, and a valve to selectively connect one of two sources of fluid to the heat exchanger, one of the two sources being at a higher temperature for providing heating fluid to the heat exchanger, and a second of the sources being at a lower temperature to provide cooling fluid to the heat exchanger; and    (2) a method of maintaining the battery pack, the battery pack including a set of battery modules, and a liquid heat exchanger comprising: determining whether the battery modules need heating or cooling; communicating a first source of fluid to the heat exchanger that will tend to be at a higher temperature when it is determined that the battery modules need heating; and communicating a second source of fluid that will tend to be at a lower temperature to the heat exchanger when it is determined that the battery modules need cooling.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a battery pack including a fan structure.    Battery pack (20)    Multi-cell battery modules (22, 24)    Electric motors (26)    Battery management system (28)    Fan control (30)    Disconnect (32)    Central fans (34, 36)    Housing (50)    Liquid heat exchanger (100)    Engine cooling loops (102)    Electric drive cooling loop (104)    Solenoid valve control (106)