In a solid polymer fuel cell series, various circumstances can result in a fuel cell being driven into voltage reversal. The pivot pin is biased inwardly by a coil spring which permits outward movement of the cover to a position in which it can be rotated downwardly out of alignment with the access opening. The locking mechanism has a central axle with a pawl that communicates with the axial hole. Exemplary button functionalities are described for an electronic device with a display, a rotatable and depressible input mechanism, andor a button. A necessary increase in the current operating level is estimated for at least each of the current local mobile units.