Abstract A Bioelectrochemical System (BES) is used for charging an electrochemical fuel to be used in a Redox Flow Cell (RFC), demonstrating the first proof of concept of a microbially-charged electrochemical fuel. Geobacter sulfurreducens, electroactive bacteria, was used to charge anthraquinone-2,6-disulfonate (2,6-AQDS) producing current densities of ca. 200–500 mA m−2 and maximum power densities of ca. 33 mW m−2. The microbially-charged electrochemical fuel and potassium ferricyanide, K3[Fe(CN)6] were introduced in a RFC producing a potential difference of 0.62 V, with a ca. 80% energy conversion efficiency. The use of a BES for charging the posilyte of a RFC is now envisioned. The bio-conversion of waste biomass energy into electrochemical fuels (microbially-charged electrochemical fuel for negalyte and posilyte) for later use in a RFC to produce electricity is a promising approach of converting biomass into storable and easy to use energy.