The present application relates to a battery case, a battery and an electronic device. The battery case comprises an upper case and a lower case, wherein a side wall of the lower case is provided with a flange; the upper case has a recessed structure and a flange; and the flange of the upper case comes in contact with the flange of the lower case, so that when the upper case and the lower case are welded, a melt, obtained after the two flanges are molten, flows into the recessed structure of the upper case. Compared with an existing battery case, in the present application, the recessed structure and the flange are provided on the upper case of the battery, such that when the case is welded, the space occupied by the melt does not exceed the battery case, thereby reducing the volume for accommodating the entire battery, so that the energy density of the battery can be increased.