An energy storage system for vehicle comprising: a lower housing; an upper housing, the lower housing and the upper housing connecting with each other; and a plurality of battery modules contained in an internal space defined by the lower housing and the upper housing, the plurality of battery modules being connected in serial or in parallel to supply power to a battery-power driven motor of the vehicle, wherein the lower housing and the upper housing connect with each other via a plurality of bolts and nuts screwed onto the respective bolts; and wherein the energy storage system for vehicle further comprises at least one frame element, the plurality of bolts pass through the at least one frame element so that the at least one frame element bears and absorbs a tightening force of the bolts in an axial direction caused by screwing the nut onto the bolt, wherein the at least one frame element comprises a first frame element having a notch (17 a) opening toward its bottom and a second frame element having a notch opening toward its top, the upper edge of the lower housing is inserted into the notch of the first frame element and the lower edge of the upper housing is inserted into the notch of the second frame element, the bolts pass through a through hole in the first frame element and a respective through hole in the second frame element, or wherein a first flange extends outwardly from and surrounds the upper edge of the body of the lower housing, the at least one frame element comprises a first frame element having a notch opening toward its side adjacent to the first flange and a second frame element having a notch opening toward its side adjacent to an edge of the upper housing, the first flange of the lower housing is inserted into the notch of the first frame element and the edge of the upper housing is inserted into the notch of the second frame element, the bolts pass through a through hole in the first frame element and a respective through hole in the second frame element. a lower housing; an upper housing, the lower housing and the upper housing connecting with each other; and a plurality of battery modules contained in an internal space defined by the lower housing and the upper housing, the plurality of battery modules being connected in serial or in parallel to supply power to a battery-power driven motor of the vehicle, wherein the lower housing and the upper housing connect with each other via a plurality of bolts and nuts screwed onto the respective bolts; and wherein the energy storage system for vehicle further comprises at least one frame element, the plurality of bolts pass through the at least one frame element so that the at least one frame element bears and absorbs a tightening force of the bolts in an axial direction caused by screwing the nut onto the bolt, wherein the at least one frame element comprises a first frame element having a notch (17 a) opening toward its bottom and a second frame element having a notch opening toward its top, the upper edge of the lower housing is inserted into the notch of the first frame element and the lower edge of the upper housing is inserted into the notch of the second frame element, the bolts pass through a through hole in the first frame element and a respective through hole in the second frame element, or wherein a first flange extends outwardly from and surrounds the upper edge of the body of the lower housing, the at least one frame element comprises a first frame element having a notch opening toward its side adjacent to the first flange and a second frame element having a notch opening toward its side adjacent to an edge of the upper housing, the first flange of the lower housing is inserted into the notch of the first frame element and the edge of the upper housing is inserted into the notch of the second frame element, the bolts pass through a through hole in the first frame element and a respective through hole in the second frame element.