Extended cycling of a soluble lead acid battery can lead to problems due to an imbalance in the coulombic efficiency leading to deposits of Pb and PbO2 on the electrodes. Periodic addition of hydrogen peroxide to the electrolyte of the soluble lead acid flow battery largely overcomes several operational problems seen during extended cycling, using a 10cm×10cm parallel plate flow cell. It is shown that this treatment greatly extends the number of cycles that can be achieved with a reasonable energy-, voltage-, and charge efficiency of 54–66%, 71%, and 77–91%.