Patent ID: 7554293

Claim:
An electric charging apparatus being attachable to a printer that is driven with electric power supplied from said electric charging apparatus while said electric charging apparatus is attached to the printer, said electric charging apparatus comprising: a battery; an electric power input unit configured to input a driving voltage based on a commercial power source; a power source relay unit configured to output a higher voltage of the driving voltage output by said electric power input unit and an output voltage of said battery; a terminal configured to supply the voltage output from said battery power source relay unit to the printer while said electric charging apparatus is attached to the printer; a reception unit configured to receive, from the printer, residual capacity information corresponding to a battery residual capacity of said battery, in a case that said electric charging apparatus is attached to the printer and said power source relay unit outputs the output voltage from said battery; a display unit configured to display the battery residual capacity of said battery; and a display control unit configured to cause said display unit to display the battery residual capacity of said battery based on the residual capacity information received from the printer by said reception unit, wherein the residual capacity of said battery is detected by the printer based on the electric power being supplied via said terminal from said power source relay unit to the printer while the electric charging apparatus is attached to said printer.