How do batteries store and release energy?

Inside a battery, two electrodes are separated by an electrolyte that allows ions to move. During discharge, chemical reactions at the electrodes create a flow of electrons through the external circuit and ions inside the battery. This converts stored chemical energy into electrical energy that powers phones, cars, and other devices. Rechargeable batteries reverse the process when connected to a charger, restoring the chemical state. Lithium-ion batteries, first commercialized in the early 1990s, dominate portable electronics because they have high energy density and can be recharged many times.