NOVELTY - The battery pack (10) has one or more battery modules, each battery module including one or more battery cells. A cover (300) accommodates the battery modules. The pack has a circulative fluid channel that is associated with the cover and through which a cooling fluid including air, water, a refrigerant, or ethanol and glycerin flows. The cover has an outer cover and an inner cover located within the outer cover and spaced apart from the outer cover. The circulative fluid channel is between the outer cover and the inner cover and contacts an inner surface of cover.    USE - Battery pack for use in electric car or hybrid car. Can also be used in high-tech electronic device e.g. cellular phone, notebook computer and camcorder.    ADVANTAGE - The internal heat is emitted to an exterior of the battery pack due to fluid circulation, thus improving the cooling characteristics of the battery pack since the battery pack can absorb and emit internal heat outward by using the circulative fluid channel or a circulative pipe on the cover through which a cooling fluid flows, thus the battery pack can efficiently dissipate internal heat. The cooling fluid that flows through the circulative fluid channel can absorb more heat if an area in which the circulative fluid channel contacts the internal space of the battery pack is increased, thus the cooling efficiency of the battery pack due to the cooling fluid circulating in the circulative fluid channel can be improved. The cover can be detachably coupleable to the holder so as to accommodate the battery modules, thus the cover can protect the battery modules from an outer environment. The battery pack has the separable cover so as to easily exchange and/or refill the cooling fluid at a certain place, e.g., an electricity charging station, thus the cooling characteristics of the battery pack can be improved and/or restored.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of a battery pack.    Battery pack (10)    Holder (200)    Cover (300)