A battery pack includes a plurality of compartments filled with an inert gas and sealed in a thermally conductive casing, a plurality of battery units each comprising rechargeable batteries and each stored in one of the plurality of compartments, internal heat-exchange systems each of which can circulate the inert gas to exchange heat with the rechargeable batteries in the one of the plurality of compartments, and an external heat-exchange system positioned outside the thermally conductive casing which can exchange heat with the thermally conductive casing surrounding the one of the plurality of compartments.