Disclosed herein is a battery pack including two or more battery modules connected to each other, external input and output terminals being formed at one side of each of the battery modules, each of the battery modules including a plurality of unit cells electrically connected to each other while being stacked, wherein the two or more battery modules are connected in series or in parallel to each other via a connection member such that one of the battery modules is connected to an adjacent one of the battery modules, and the connection member is configured to have a structure in which different kinds of metals having different melting points are coupled to each other.