What chemical changes occur when a storage battery is discharged?

When a storage battery discharges, it converts stored chemical energy into electrical energy through oxidation-reduction (redox) reactions occurring at the electrodes.12

During this process, the following chemical changes take place:

• Electron Transfer: The anode (negative electrode) undergoes oxidation, meaning it gives up electrons. These electrons flow through an external circuit to the cathode (positive electrode), where they are accepted by the cathode material, which is reduced to a less-oxidized state.34
• Ion Movement: To maintain electrical neutrality, ions within the electrolyte move between the electrodes, balancing the flow of electrons in the external circuit.32
• Material Consumption: The active chemical materials at both electrodes are consumed or transformed into different compounds. For example, in a lead-acid battery, lead dioxide at the positive electrode and lead at the negative electrode both react with the sulfuric acid electrolyte to produce lead sulfate and water.5
• Electrolyte Alteration: As chemical reactions consume components of the electrolyte, its composition changes—often becoming more dilute—which can be used to measure the battery's state of charge.5