Like metal ions our polymers can store electric energy by taking up/releasing electrons. Unlike conventional batteries the P-RFB does not use solid battery cells of a predefined size but a scalable system consisting of two components: Reservoir tanks (I) and an electrochemical cell (II). The energy storage polymer developed by JenaBatteries is dissolved in a water-based electrolyte, which is stored in the reservoir tanks. By varying the size of the tank the capacity of the battery can easily be tailored to individual needs. The tanks are connected to an electrochemical cell that charges/discharges the polymer with electric energy. Varying the size of the electrochemical cell adjusts the power output of the battery. By this means customized, yet extendible, energy storage solutions are created that fit the needs of various applications.