A battery, a battery assembly, and a user equipment are disclosed. The battery includes a circuit board and a cell. The circuit board includes a first contact, a second contact, a third contact, a fourth contact, a battery management module, and a control switch. The first contact reports a capacity of the cell in the battery, or in the battery and a cascaded battery to an upper-level battery or an electricity load; the second contact receives and output the capacity of the cell in the cascaded battery; when the control switch is opened, the third contact is connected to the cell in the battery to charge or discharge the cell in the battery; when the control switch is closed, the fourth contact is connected to the third contact; and the battery management module triggers opening or closing of the control switch.