A method and system for heating a vehicle battery, such as the type used for vehicle propulsion in a hybrid electric vehicle (HEV). Depending on the battery chemistry involved, such batteries may not perform well in extremely cold environments. For instance, a lithium-ion battery can exhibit a high internal resistance when the battery is extremely cold, which in turn can negatively affect the available power or other capabilities of the battery. According to an exemplary embodiment, the method and system take advantage of the high internal resistance in a cold vehicle battery by purposely cycling electrical current in and/or out of the battery so that heat is created. This heat warms up the vehicle battery and thereby improves its overall performance and capabilities.