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How do rechargeable batteries store electrical energy as chemical energy?

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Crystal growth — electrochemical reaction Different mechanisms of crystal growth.

Rechargeable batteries store electrical energy as chemical energy through reversible oxidation-reduction (redox) reactions.1

During discharge, the battery generates electric current as electrons flow from a reducing agent at the negative electrode to an oxidizing agent at the positive electrode through an external circuit. This process converts the active materials into different chemical substances.213

To store energy, a direct current (DC) voltage—greater than the battery's own—is applied in the opposite direction of the discharge. This forces electrons back through the charging circuit and into the electrodes, reversing the chemical reactions. By driving these electrons back, the battery restores its original chemical composition, energy level, and power capability.2

In systems like the lead-acid battery, this process involves the conversion of lead sulfate and water back into lead, lead dioxide, and sulfuric acid, effectively "recharging" the chemical potential of the cell.3