PROBLEM TO BE SOLVED: To enable a specific apparatus to recognize a battery residual amount of another apparatus.SOLUTION: A battery residual amount monitoring device 1 outputs a detection command to a battery residual amount monitoring target device 21 by using short-range radio communication, at periodic detection timing, during the short-range radio communication with the battery residual amount monitoring target device 21, in the case of having received notification, from another battery residual amount monitoring target device, that the device is being charged, or in the case that the battery residual amount monitoring device 1 is being charged. Receiving the detection command, the battery residual amount monitoring target device 21 transmits, as a detection battery residual amount, a battery residual amount of a battery unit 23 to the battery residual amount monitoring device 1 by using the short-range radio communication. The battery residual amount monitoring device 1 displays the received detection battery residual amount of the battery residual amount monitoring target device 21, on a display unit 4. The battery residual amount monitoring device 1 also can display, on the display unit 4, a detection battery residual amount of a battery residual amount monitoring target device 21 during being charged, by using a wide area communication network; or can display, on the display unit 4, information on a location in which a SSID of a WiFi router apparatus is received to show charge is possible in the location.
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