chemical reaction
called an alkaline battery when adapted to operate under alkaline conditions. Button batteries have a high output-to-mass ratio; lithiumiodine batteries consist of a solid electrolyte; the nickel cadmium NiCad battery is rechargeable; and the leadacid battery, which is also rechargeable, does not require the electrodes to be in separate compartments. A fuel cell requires an external supply of reactants as the products of the reaction are continuously removed. In a fuel cell, energy is not stored; electrical energy is provided by a chemical reaction.