A battery case, characterized in that , comprising: a bottom plate ; and a plurality of extensions (a) circumferentially spaced, the extensions (a) being formed by extending horizontally outward along the bottom plate , wherein each of the extensions (a) is bended at least once to form a case side arm and a cavity of the battery case is enclosed by the case side arms and the bottom plate , and wherein end faces for connection of the case side arms are bended to form connecting portions, and two adjacent connecting portions are snap-fitted to fix the adjacent case side arms to each other; wherein the connecting portions comprise first connecting portions and second connecting portions ; the case side arms comprise: at least two end plates , end faces for connection of the end plates being bended to form the first connecting portions ; and at least two side plates , an end plate being arranged between the adjacent side plates , end faces for connection of the side plates being bended to form the second connecting portions ; and adjacent first connecting portion and second connecting portion are snap-fitted together; wherein the end faces, facing away from the bottom plate , of the side plates extend outward to form pressing members , and the pressing members are located inside the cavity of the battery case. a bottom plate ; and a plurality of extensions (a) circumferentially spaced, the extensions (a) being formed by extending horizontally outward along the bottom plate , wherein each of the extensions (a) is bended at least once to form a case side arm and a cavity of the battery case is enclosed by the case side arms and the bottom plate , and wherein end faces for connection of the case side arms are bended to form connecting portions, and two adjacent connecting portions are snap-fitted to fix the adjacent case side arms to each other; wherein the connecting portions comprise first connecting portions and second connecting portions ; the case side arms comprise: at least two end plates , end faces for connection of the end plates being bended to form the first connecting portions ; and at least two side plates , an end plate being arranged between the adjacent side plates , end faces for connection of the side plates being bended to form the second connecting portions ; and adjacent first connecting portion and second connecting portion are snap-fitted together; wherein the end faces, facing away from the bottom plate , of the side plates extend outward to form pressing members , and the pressing members are located inside the cavity of the battery case. at least two end plates , end faces for connection of the end plates being bended to form the first connecting portions ; and at least two side plates , an end plate being arranged between the adjacent side plates , end faces for connection of the side plates being bended to form the second connecting portions ; and adjacent first connecting portion and second connecting portion are snap-fitted together; wherein the end faces, facing away from the bottom plate , of the side plates extend outward to form pressing members , and the pressing members are located inside the cavity of the battery case. <EOS>