NOVELTY - The method involves reversing a flow direction of a circulatable heat transfer medium (26) e.g. air and water/glycol mixture, by a temperature control circuit according to a predetermined time interval or a temperature of a moderate temperature-requiring unit (20). Inlet temperature of the medium is kept higher than a target temperature of the unit when an actual temperature of the unit is kept lower than the target temperature. The inlet temperature of the medium is kept lower than the target temperature of the unit when the actual temperature of the unit exceeds the target temperature.    USE - Method for keeping a moderate temperature-requiring unit utilized for supplying power to various appliances, at a moderate temperature, during an electrochemical process, a chemical process and/or a physical process. Uses include but are not limited to a battery, a capacitor, a capacitor battery and fuel cells e.g. lithium ion cells, nickel metal hydride cells or lithium polymer cells, for a portable electric appliance e.g. mobile telephone, laptop, camcorder, MPEG-1 Audio Layer 3 player, an electric vehicle such as plug-into hybrid electric vehicle and hybrid electric vehicle, or electric bike and a stationary plant such as photovoltaic plant or a network buffer.    ADVANTAGE - The method enables keeping the inlet temperature of the heat transfer medium higher and lower than the target temperature of the unit based on the actual temperature of the unit, so that a homogeneous temperature distribution in a fluid temperature body or moderate temperature-requiring unit can be achieved.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a device for keeping a moderate temperature-requiring unit at a moderate temperature.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic perspective view of a moderate temperature-requiring unit with multiple moderate temperature-requiring components that are reversible in a direction of a heat transfer medium.    Moderate temperature-requiring unit (20)    Moderate temperature-requiring components (21-25)    Circulatable heat transfer medium (26)