In a battery, how is the energy usually stored

In batteries, energy is stored in the form of chemical energy. When connected in a circuit, the chemical energy is released as electrical energy. Inside the battery, there is a liquid or a gel-like substance that has electrically charged ions. The materials that make up the electrodes of the battery combine with the charged ions, producing chemical reactions that allow movement of electrons generating an electric current. However the reactions take place only if the two ends of the electrode are linked in a circuit.

Exothermic,  physical change after it is already baked