NOVELTY - A hybrid redox flow battery capable of operating in power delivery mode comprises 1st reversible electrode in a 1st electrode compartment (4) containing 1st aqueous electrolyte, 2nd reversible electrode (10) in a 2nd electrode compartment (6) containing 2nd aqueous electrolyte, and conduit arrangement configured, in power delivery mode, for carrying electrochemically active species to 1st electrode and, in an energy storage mode, for carrying generated electrochemically active species away from 1st electrode.    USE - A hybrid redox flow battery (HyRFB) capable of operating in a power delivery mode.    ADVANTAGE - The battery may reduce or prevent metal dendrite formation, or reduce or eliminate cross contamination, may be cheaper and have higher power density and/or energy density than commercial devices for generating and storing electricity.    DETAILED DESCRIPTION - A hybrid redox flow battery capable of operating in power delivery mode comprises 1st reversible electrode in a 1st electrode compartment containing 1st aqueous electrolyte, 2nd reversible electrode in a 2nd electrode compartment containing 2nd aqueous electrolyte, and conduit arrangement configured, in power delivery mode, for carrying electrochemically active species to 1st electrode and, in an energy storage mode, for carrying generated electrochemically active species away from 1st electrode. The 2nd electrode contains alkali metal ions or alkaline earth metal ions and a material which can reversibly take up and release alkali metal ions or alkaline earth metal ions during modes of operation. The battery generates electrical power by reaction of electrochemically active species at 1st and 2nd electrode and in an energy storage mode in which it consumes electrical power to generate at least greater than or equal to 1 electrochemically active species. INDEPENDENT CLAIMS are included for:    (1) hybrid redox flow battery in which the material of the 2nd electrode is a divalent cation solid state insertion material of formula AMx(Fe2+(CN)6)2x(Fe3+(CN6))1-2x; and    (2) operation of hybrid redox flow battery in (a) a power delivery mode in which it generates electrical power by the reaction of electrochemically active species at an anode and at a cathode, and (b) in an energy storage mode in which it consumes electrical power to generate greater than or equal to 1 electrochemically active species.    A=Ba, Sr, Ca, and/or Mg; and    M=Ni and/or Cu.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of a hybrid redox flow battery.    2nd conduit (1)    Material of 2nd electrode (3)    1st electrode compartment (4)    2nd electrode compartment (6)    2nd reversible electrode (10)