HOW BATTERIES WORK: Any battery converts chemical energy into electricity. There are two ends, called terminals: one is positively charged, while the other is negatively charged. Opposite charges attract. So when these two ends are connected by a metallic wire, electrons will flow from the negatively charged terminal to the positively charged one. This flow makes an electric current in the wire. The current can be used for power, simply by attaching a light bulb, for example. A battery continually produces new electrons at the negative terminal from a series of chemical reactions. So the battery essentially acts like a pump, pulling electrons from the negative end of the conducting wire and pushing them into the positive end. A battery only holds a certain amount of reactants. Once those are used up, there can be no more chemical reactions, and the battery is dead.
The American Physical Society contributed to the information contained in the TV portion of this report.