Batteries and also fuel cells: One among the oldest and most important functions of electrochemistry is always to the storage and conversion of energy. You already know that a galvanic cell transforms chemical energy to work; similarly, an electrolytic cell transforms electrical work into chemical free energy. Devices that perform these conversion rates are called batteries. In common batteries the chemicalcomponents are provided within the device by itself. If the reactants are supplied from an external source since they are consumed, the device is called a fuel cell.