A battery module, comprising: a plurality of battery cells arranged in a row; a plurality of bus bars connecting electrical terminals of adjacent cells so that the plurality of battery cells are in series; and a short circuit member that is mechanically connected to a first battery cell among the plurality of battery cells and that is electrically connected to an electrical terminal of a second battery cell among the plurality of battery cells in the same row; wherein the first battery cell further includes a membrane that is electrically short-circuitable to the short circuit member, in response to an overcharge of the battery module; wherein the short circuit member includes: a base region that is mechanically connected to a side wall of the first battery cell; a first extension region that extends from the base region and whose end overlies the membrane of the first battery cell; and a second extension region that extends from the base region and that is electrically connected to an electrical terminal of the second battery cell; whereby a short-circuit between the second battery cell and the membrane may be formed by the second extension region, the base region and the first extension region in series; characterised in that each of the first and second battery cells (100a, 100b) includes an electrode assembly, a case accommodating the electrode assembly, and a first terminal and a second terminal passing through the case and outwardly extending from the electrode assembly, the case includes a long sidewall and a short sidewall, the short sidewall having smaller area than an area of the long sidewall, the base region of the short circuit member is on the long sidewall, and the area of the long sidewall is about equal to an area of the base region. a plurality of battery cells arranged in a row; a plurality of bus bars connecting electrical terminals of adjacent cells so that the plurality of battery cells are in series; and a short circuit member that is mechanically connected to a first battery cell among the plurality of battery cells and that is electrically connected to an electrical terminal of a second battery cell among the plurality of battery cells in the same row; wherein the first battery cell further includes a membrane that is electrically short-circuitable to the short circuit member, in response to an overcharge of the battery module; wherein the short circuit member includes: a base region that is mechanically connected to a side wall of the first battery cell; a first extension region that extends from the base region and whose end overlies the membrane of the first battery cell; and a second extension region that extends from the base region and that is electrically connected to an electrical terminal of the second battery cell; whereby a short-circuit between the second battery cell and the membrane may be formed by the second extension region, the base region and the first extension region in series; characterised in that each of the first and second battery cells (100a, 100b) includes an electrode assembly, a case accommodating the electrode assembly, and a first terminal and a second terminal passing through the case and outwardly extending from the electrode assembly, the case includes a long sidewall and a short sidewall, the short sidewall having smaller area than an area of the long sidewall, the base region of the short circuit member is on the long sidewall, and the area of the long sidewall is about equal to an area of the base region. a base region that is mechanically connected to a side wall of the first battery cell; a first extension region that extends from the base region and whose end overlies the membrane of the first battery cell; and a second extension region that extends from the base region and that is electrically connected to an electrical terminal of the second battery cell; whereby a short-circuit between the second battery cell and the membrane may be formed by the second extension region, the base region and the first extension region in series; characterised in that each of the first and second battery cells (100a, 100b) includes an electrode assembly, a case accommodating the electrode assembly, and a first terminal and a second terminal passing through the case and outwardly extending from the electrode assembly, the case includes a long sidewall and a short sidewall, the short sidewall having smaller area than an area of the long sidewall, the base region of the short circuit member is on the long sidewall, and the area of the long sidewall is about equal to an area of the base region.