A battery system comprising: a battery block including a plurality of square battery cells stacked in one direction, each of the plurality of square battery cells having a discharge port provided with a discharge valve that opens at a set pressure and a sealing plate provided with positive and negative electrode terminals via an insulating material; a parallel connection bus bar configured to be connected to an electrode terminal of each of the plurality of square battery cells and connect some or all of the plurality of square battery cells in parallel with each other; an insulating plate disposed on a surface of the sealing plate of each of the plurality of square battery cells, the insulating plate including a passing portion provided at positions corresponding to the discharge port and having an opening that pass exhaust gas ejected from the discharge port and a pressing portion disposed between the parallel connection bus bar and the sealing plate; and a lid plate fixed to the insulating plate and facing the discharge port facing the opening of the passing portion; characterised in that: the battery block includes a plurality of parallel-connected units, formed by connecting the square battery cells in parallel, connected to each other in series, and the insulating plate is provided with a plurality of slits between adjacent parallel-connected units among the plurality of parallel-connected units so as to have the plurality of slits extending in a width direction of the square battery cells; wherein the lid plate and the insulating plate are connected between adjacent slits among the plurality of slits, and a coupling position where the lid plate and the insulating plate are connected, being the coupling position between the adjacent slits is eccentrically located from a center of the discharge port in the width direction of the square battery cells. a battery block including a plurality of square battery cells stacked in one direction, each of the plurality of square battery cells having a discharge port provided with a discharge valve that opens at a set pressure and a sealing plate provided with positive and negative electrode terminals via an insulating material; a parallel connection bus bar configured to be connected to an electrode terminal of each of the plurality of square battery cells and connect some or all of the plurality of square battery cells in parallel with each other; an insulating plate disposed on a surface of the sealing plate of each of the plurality of square battery cells, the insulating plate including a passing portion provided at positions corresponding to the discharge port and having an opening that pass exhaust gas ejected from the discharge port and a pressing portion disposed between the parallel connection bus bar and the sealing plate; and a lid plate fixed to the insulating plate and facing the discharge port facing the opening of the passing portion; the battery block includes a plurality of parallel-connected units, formed by connecting the square battery cells in parallel, connected to each other in series, and the insulating plate is provided with a plurality of slits between adjacent parallel-connected units among the plurality of parallel-connected units so as to have the plurality of slits extending in a width direction of the square battery cells; wherein the lid plate and the insulating plate are connected between adjacent slits among the plurality of slits, and a coupling position where the lid plate and the insulating plate are connected, being the coupling position between the adjacent slits is eccentrically located from a center of the discharge port in the width direction of the square battery cells.