An electric window covering comprising: a motorized assembly, which controls a movement of a covering material of the electric window covering; a power supply device, which comprises a rechargeable power unit and a first remaining power detection circuit, wherein the rechargeable power unit is coupled to and provides power to the motorized assembly, and the first remaining power detection circuit is coupled to the rechargeable power unit to detect a potential magnitude of the rechargeable power unit and to generate and output a potential signal; a comparison module coupled to the first remaining power detection circuit, wherein the potential signal outputted by the first remaining power detection circuit is inputted into the comparison module; when the potential magnitude represented by the potential signal is less than a threshold predetermined in the comparison module, the comparison module generates and outputs a warning notice signal; and a notification unit comprising a presenting module, wherein the presenting module receives the warning notice signal and represents a warning notice representing the warning notice signal; characterized in that said electric window covering further comprising: a portable charging device configured to be detachably coupled to and provide power saved in the portable charging device to the rechargeable power unit, the portable charging device comprising an electric power output; a first fixing structure disposed at the portable charging device; a frame; a second fixing structure disposed at the frame; and an electric power input disposed at the frame and coupled to the rechargeable power unit; wherein when the first fixing structure and the second fixing structure are connected, the electric power output provides the power to the rechargeable power unit through the electric power input, when the first fixing structure and the second fixing structure are separated, the electric power output stops providing the power to the rechargeable power unit. a motorized assembly, which controls a movement of a covering material of the electric window covering; a power supply device, which comprises a rechargeable power unit and a first remaining power detection circuit, wherein the rechargeable power unit is coupled to and provides power to the motorized assembly, and the first remaining power detection circuit is coupled to the rechargeable power unit to detect a potential magnitude of the rechargeable power unit and to generate and output a potential signal; a comparison module coupled to the first remaining power detection circuit, wherein the potential signal outputted by the first remaining power detection circuit is inputted into the comparison module; when the potential magnitude represented by the potential signal is less than a threshold predetermined in the comparison module, the comparison module generates and outputs a warning notice signal; and a notification unit comprising a presenting module, wherein the presenting module receives the warning notice signal and represents a warning notice representing the warning notice signal; characterized in that said electric window covering further comprising: a portable charging device configured to be detachably coupled to and provide power saved in the portable charging device to the rechargeable power unit, the portable charging device comprising an electric power output; a first fixing structure disposed at the portable charging device; a frame; a second fixing structure disposed at the frame; and an electric power input disposed at the frame and coupled to the rechargeable power unit; wherein when the first fixing structure and the second fixing structure are connected, the electric power output provides the power to the rechargeable power unit through the electric power input, when the first fixing structure and the second fixing structure are separated, the electric power output stops providing the power to the rechargeable power unit. a portable charging device configured to be detachably coupled to and provide power saved in the portable charging device to the rechargeable power unit, the portable charging device comprising an electric power output; a first fixing structure disposed at the portable charging device; a frame; a second fixing structure disposed at the frame; and an electric power input disposed at the frame and coupled to the rechargeable power unit; wherein when the first fixing structure and the second fixing structure are connected, the electric power output provides the power to the rechargeable power unit through the electric power input, when the first fixing structure and the second fixing structure are separated, the electric power output stops providing the power to the rechargeable power unit.