9.5 Parts of a Battery
All batteries have two electrodes: an anode and a cathode. These are usually made of different types of metals. They are separated by an electrolyte, which is a liquid in a wet-cell battery and a solid or a paste in a dry-cell battery. The battery produces an electric current by attaching wires with an electrical load to the anode and cathode, which will cause positively-charged ions to flow across the electrolyte from the anode to the cathode and electrons to move through the wires in the same direction.
A battery is called “dead” when all of the chemical energy of the reactions of the anode and cathode has been used up. Some batteries can be recharged because the reactions that power them are reversible and the presence of an electric current will cause them to reverse direction and build up chemical energy again. Other batteries are powered by non-reversible reactions, so these types can’t be recharged once they’re drained.