NOVELTY - Operating a portable device comprising a power system housed within the device comprises providing flow cells; introducing the flowable redox composition from the dispensing vessel into electroactive zone(s) to cause the flow cell to discharge to provide electric energy to operate the device; and receiving the discharged redox composition in the receiving vessel.    USE - Method for operating a portable device (including vehicle or portable power generator) comprising a power system housed within the device (claimed).    DETAILED DESCRIPTION - Operating a portable device comprising a power system housed within the device comprises providing flow cells; introducing the flowable redox composition from the dispensing vessel into electroactive zone(s) to cause the flow cell to discharge to provide electric energy to operate the device; and receiving the discharged redox composition in the receiving vessel. Each flow cell comprises a positive electrode current collector, a negative electrode current collector, an ion-permeable membrane separating the positive and negative current collectors, dispensing vessel(s), and receiving vessel(s). The positive electrode current collector and the ion-permeable membrane define a positive electroactive zone for accommodating a positive electroactive material. The negative electrode current collector and the ion-permeable membrane define a negative electroactive zone for accommodating a negative electroactive material. Positive and negative electroactive material(s) comprises a flowable redox composition in the electroactive zone. The dispensing vessel is provided for dispensing a flowable redox composition into the positive or negative electroactive zone. It is connected with the flow cells and in fluidic communication with the electroactive zone and the dispensing vessel is capable of being connected and disconnected from the flow cell. The receiving vessel is provided for receiving flowable redox composition from the positive or negative electroactive zone, where the receiving vessel is connected with the flow cell and in fluidic communication with the electroactive zone and the receiving vessel is capable of being connected and disconnected from the flow cell.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of a multi-redox flow cell stack.    Anode storage tank (1102)    Bladders (1103, 1105)    Cathode storage tank (1104)    Reversible flow pump (1106)    Flow valve (1118, 1121)