NOVELTY - The flow battery comprises: a first half-cell comprising a first aqueous electrolyte that includes a first redox active material and a first carbon electrode present in contact with the first aqueous electrolyte; a second half-cell comprising a second aqueous electrolyte that includes a second redox active material and a second carbon electrode present in contact with the second aqueous electrolyte; and a separator (30) disposed between the first half-cell and the second half-cell. The first half-cell has a half-cell potential of greater than or equal to -0.40 V with respect to a reversible hydrogen electrode.    USE - The flow battery is useful in a system for providing stable power for remote camps, forward operating bases, off-grid telecommunications and/or remote sensors (all claimed), where the system is an electrochemical energy storage system, and the flow battery is a regenerative fuel cell, reversible fuel cell or flow energy device.    ADVANTAGE - The flow battery is safe, inexpensive, easy to use and reliable, improves performance, decoupling energy and power, system scalability, round trip energy efficiencies and cycle life of the system, and can be efficiently operate at high voltages.    DETAILED DESCRIPTION - The flow battery comprises: a first half-cell comprising a first aqueous electrolyte that includes a first redox active material and a first carbon electrode present in contact with the first aqueous electrolyte; a second half-cell comprising a second aqueous electrolyte that includes a second redox active material and a second carbon electrode present in contact with the second aqueous electrolyte; and a separator (30) disposed between the first half-cell and the second half-cell. The first half-cell has a half-cell potential of greater than or equal to -0.40 V with respect to a reversible hydrogen electrode. The first aqueous electrolyte has a pH of 10-12. The flow battery operates at a current density of 50 mA/cm2. The redox active materials do not plate onto the carbon electrodes during operation of the flow battery. The flow battery has an energy density of 30 watt hour/liter. The second half-cell has a potential of +1.10 V with respect to a reversible hydrogen electrode. The first and the second half-cells exhibit reversible electrochemical kinetics. The flow battery exhibits essentially zero hydrogen evolution current when operates at a current density of 50 mA/cm2. The carbon electrodes remain essentially metal free during operation of the flow battery. The flow battery further comprises: a first-electrolyte tank present in fluidic communication with a first chamber; a second-electrolyte tank present in fluidic communication with a second chamber; and a pump (60) for transporting a fluid between the second-electrolyte tank and the second chamber or between the first-electrolyte tank and/or the first chamber. INDEPENDENT CLAIMS are included for:    (1) a method for charging the flow battery;    (2) a method for discharging the flow battery;    (3) a method for operating the flow battery; and    (4) an electrochemical energy storage system.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a flow battery.    Electrode (10)    Separator (20)    First redox material (30)    Second active material (40)    Pump. (60)