An electric window covering is disclosed, which has a motorized assembly for controlling a movement of a covering material, a rechargeable battery for providing electric power to the motorized assembly, an electric power input at an overhead frame coupled with the rechargeable battery, and a separable charging device. The separable charging device has an electrical connector, a conductor and an electric power output provided at an extension object for charging the rechargeable battery through the electric power input. The separable charging device further has a first fixing structure at the extension object adapted to engage with a second fixing structure at the overhead frame for charging the rechargeable battery. After the extension object and the overhead frame are disengaged, the rechargeable battery still provides electric power to the motorized assembly for controlling the movement of the covering material.