The invention discloses a device and a method of self-testing battery performance. The device comprises a charging administrative unit, an internal-resistance-measuring unit and a switch-controlling unit. The charging administrative unit is used for charging a battery and triggering the switch-controlling unit when the process of charging battery is started and finished. The switch-controlling unit is used for controlling the inner-resistance-measuring unit to disconnect with the battery when the battery begins to be charged and controlling the inner-resistance-measuring unit to connect with the battery when the process of charging the battery is finished. The inner-resistance-measuring unit is used for connecting the battery and measuring the inner resistance of the battery and recording the inner resistance value and gaining a plurality of the inner resistance values after experiencing a plurality of records of charging the battery and predicating the maximum charging time of the inner resistance far from being scrapped. The device enables the users to know visually the battery at what level through the display from the screen by increasing the inner-resistance-measuring unit on the terminal.