An apparatus for covering an open top of a transportation trailer container, such as a chip train carrying wood chips, is provided. A flexible cover (e.g. tarp) may be deployed and retracted using a roller moved overtop of the container using pivotable arms. An electrically powered covering mechanism automatically deploys and retracts the cover. The covering mechanism is powered by a supercapacitor, which is charged when connected to an external power source. A charging control circuit can selectably allow or inhibit charging of the supercapacitor depending on power demands of other electrical loads.