The present invention provides a backup battery box for electric cylinder, which is assembled and electrically connected with the control box for driving the operation of the electric cylinder. The present invention comprises: a charge/discharge device and a rechargeable battery. The charge/discharge device comprises: a protection unit, a power conversion unit, a voltage detection unit, a control unit, a discharge unit, a display unit and a switch unit. The rechargeable battery and the charge/discharge device are electrically connected. When the start button of the switch unit is pressed, the charge/discharge device may transfer the electricity in the rechargeable battery to the control box. When the power-off button of the switch unit is pressed, the charge/discharge device will be in a power-off mode to prevent the electricity of the backup battery to be exhausted.一種電動缸的備用電池盒，係與該控制盒組裝並電性連結，用以驅動電動缸動作，包括：一充放電裝置及一充電電池。該充放電裝置包含有：一保護單元、一電源轉換單元、一電壓偵測單元、一控制單元、一放電單元、一顯示單元及一開關單元。該充電電池與該充放電裝置電性連結。該開關單元的啟動開關按下時，由該充放電裝置將該充電電池的電力傳輸至控制盒中。在該開關單元的斷電開關按下時，該充放電裝置呈不供電模式，使備用電池盒的電力不被耗盡。
