Batteries

In 1786, an Italian physician, physicist and philosopher Luigi Aloisio Galvani (September 9, 1737 December 4, 1798) discovered that when touching frogs legs with two different metals they would twitch, so it was assumed that the frogs contained electricity, and at the time it was well known that electricity could make muscles move. However, Galvani's theory was wrong, and another Italian physicist Count Alessandro Volta, (February 18 1745 March 5 1827) discovered the right answer in 1800's. Electricity could be produced by a combination of two different metals and a solution that would conduct electricity. In Galvani's experiments, the frog's legs had sufficient moisture, but Volta showed that the salt/brine solution was more effective. Using one copper and one zinc disc, separated by a piece of cloth moistened in the salt soaked solution. Volta made the first electric cell, but this produced only a weak current. However, he found out that he could obtain a stronger current by stacking several cells, which became the first practical battery and a source of portable electricity.

Since Volta's first battery, many different types of electrical cell have been invented. But the basic principle of operation is the same in each case. Current is made by the flow between two electrodes composed of different materials. Separating the electrodes is a solution called electrolyte. Even dry cell batteries contain a liquid in the form of a paste. When the two electrodes are connected together by a wire or electrical conductor, reactions take place at the electrodes. In one electrode, a surplus of electrons is produced. These flow through the circuit, from one electrode to the other as a current.

When a cell is in use, the reactions that take place in it gradually change the nature of the electrolyte. Eventually the cell runs out and no longer supplies a useful current. In the case of primary batteries, the only remedy is to replace them. But, secondary cells can be recharged. Rechargeable batteries can be connected to a mains unit, a power distribution electrical device, in which electricity is passed through them for several hours. This has the effect of reversing the chemical reactions that have taken place during their initial use. As a result, the electrolyte is gradually restored to its original state. When this process has been completed, the cell is ready for use once again.

Secondary cells are also known as storage cells or accumulators. A typical car battery consists of six of these cells connected together. The car's generator normally keeps the battery well charged while the engine is running. However, in some cases if the battery is not in use for a length of time it will need to be recharged or replaced.

Most cars batteries are of the lead-acid type. They have electrodes of lead and lead dioxide in an electrolyte solution of diluted sulfuric acid. Some portable electrical equipment, contain small nickel cadmium storage cells. One electrode consists of nickel compounds, while the other is made of cadmium. The electrolyte is an alkali called potassium hydroxide. Equipment powered by these nickel candmium often have tiny built in mains unit, for easy recharging. If the device is left connected to the mains unit overnight by morning the cells will be fully recharged and ready for use once more.