A battery module , comprising: two or more secondary batteries arranged side by side in a first direction (X), each of which includes a case , an electrode assembly and a closing portion, wherein the case has a receiving hole comprising an opening and extending in a second direction (Y), and the first direction (X) intersects with the second direction (Y), wherein the closing portion is sealingly connected with the case to close the opening, the electrode assembly is disposed in the receiving hole and includes two or more electrode units , the electrode unit includes a first electrode plate , a second electrode plate and a separator , and the two or more electrode units are stacked in the second direction (Y), characterized in that , the electrode unit is formed by winding the first electrode plate , the second electrode plate and the separator , and the electrode unit is formed into a flat shape and has two wide sides and two narrow sides , wherein the two narrow sides are connected to two opposite ends of the wide side in the first direction (X) respectively, the wide side is disposed opposite to the closing portion, and the wide side has an area larger than that of the narrow side ; and the case comprises a first side wall , a second side wall and a bottom wall connected to the first side wall and the second side wall , wherein the first side wall has a larger area than the second side wall and the bottom wall , adjacent two secondary batteries are disposed with the first side walls not the second side walls opposite to each other, and the narrow side of the electrode unit is disposed corresponding to the first side wall . two or more secondary batteries arranged side by side in a first direction (X), each of which includes a case , an electrode assembly and a closing portion, wherein the case has a receiving hole comprising an opening and extending in a second direction (Y), and the first direction (X) intersects with the second direction (Y), wherein the closing portion is sealingly connected with the case to close the opening, the electrode assembly is disposed in the receiving hole and includes two or more electrode units , the electrode unit includes a first electrode plate , a second electrode plate and a separator , and the two or more electrode units are stacked in the second direction (Y), characterized in that , the electrode unit is formed by winding the first electrode plate , the second electrode plate and the separator , and the electrode unit is formed into a flat shape and has two wide sides and two narrow sides , wherein the two narrow sides are connected to two opposite ends of the wide side in the first direction (X) respectively, the wide side is disposed opposite to the closing portion, and the wide side has an area larger than that of the narrow side ; and the case comprises a first side wall , a second side wall and a bottom wall connected to the first side wall and the second side wall , wherein the first side wall has a larger area than the second side wall and the bottom wall , adjacent two secondary batteries are disposed with the first side walls not the second side walls opposite to each other, and the narrow side of the electrode unit is disposed corresponding to the first side wall . <EOS>