Batteries may seem simple, but the delivery of packaged power is a complicated electrochemical process. Electric current in the form of electrons begins to flow in the external circuit when the device-a light bulb for example-is turned on. At that time, the anode material, zinc, gives up two electrons per atom in a process called oxidation, leaving unstable zinc ions behind. After the electrons do their work powering the light bulb, they re-enter the cell at the cathode, where they combine with the active material, manganese dioxide, in a process called reduction. The combined processes of oxidation and reduction couldn't occur in a power cell without an internal way to carry electrons back to the anode, balancing the external flow of current. This process is accomplished by the movement of negatively charged hydroxide ions present in the water solution called the electrolyte. Every electron entering the cathode reacts with the manganese dioxide to form MnOO-. Then, MnOO- reacts with water from the electrolyte. In that reaction, the water splits, releasing hydroxide ions into the electrolyte and hydrogen ions that combine with MnOO- to form MnOOH. The internal circuit is completed when the hydroxide ions produced in this reaction at the cathode flow to the anode in the form of ionic current. There, they combine with unstable zinc ions, which were formed at the anode when the electrons were originally given up to the external circuit. This produces zinc oxide and water. This completes the circuit (which is necessary to have a constant flow of electricity) and powers your torch.