<p>The significant increase in the use of electronic devices resulted in an increasing amount of battery waste, especially used zinc-carbon batteries containing toxic metals and electrolytes. This situation reinforced the need for more effective recycling strategies, including the recovery of graphite and electrolyte paste for reuse as electrode materials in reverse electrodialysis systems. Reverse electrodialysis was a renewable energy technology that converted differences in salt content into electrical energy. A simple upcycling route demonstrated to converts zinc-carbon battery waste into a composite carbon electrode for reverse electrodialysis, enabling salinity-gradient energy harvesting from waste-derived materials. In this study, graphite and electrolyte paste were extracted through manual disassembly, washing, and drying, and then mixed with a polyvinyl cholride/N-methyl-2-pyrrolidone binder to create a composite electrode. Electrode characterization involved measurements of porosity, swelling degree, conductivity, and ion exchange capacity. The composition of 60% graphite and 40% electrolyte paste showed optimal performance with a dense amorphous structure, 6% porosity, and a specific surface area of 5.5 m² g^− 1. Despite the very low ion exchange capacity value (0.000326 meq g^− 1), this electrode produced a conductivity of 2.095&#xa0;S cm^− 1. Testing with a 30&#xa0;g L^− 1 sodium chloride solution showed that the power density of the electrode reached 0.024–0.027&#xa0;W m^− 2. Although the power density and current generated were lower than those of commercial graphite electrodes (0.045&#xa0;W m^− 2 and 0.013 mA m^− 2), the composite electrode maintained stable output over 20&#xa0;min test. These findings were demonstrated the potential of battery waste for clean energy applications.</p> Graphical abstract <p></p>