Batteries

In electronics, a battery or voltaic cell is a combination of one or more electrochemical Galvanic cells which store chemical energy that can be converted into electric potential energy, creating electricity. Since the invention of the first Voltaic pile in 1800 by Alessandro Volta, the battery has become a common power source for many household and industrial applications, and is now a multi-billion dollar industry. n 1791, Luigi Galvani published a report on "animal electricity." He created an electric circuit consisting of two different metals, with one touching a frog's leg and the other touching both the leg and the first metal, thus closing the circuit. In modern terms, the frog's leg served as both the electrolyte and the sensor, and the metals served as electrodes. He noticed that even though the frog was dead, its legs would twitch when he touched them with the metals.

Although early batteries were of great value for experimental purposes, in practice their voltages fluctuated and they could not provide a large current for a sustained period. Later, starting with the Daniell cell in 1836, batteries provided more reliable currents and were adopted by industry for use in stationary devices, particularly in telegraph networks where they were the only practical source of electricity, since electrical distribution networks did not then exist. These wet cells used liquid electrolytes, which were prone to leakage and spillage if not handled correctly. Many used glass jars to hold their components, which made them fragile. These characteristics made wet cells unsuitable for portable appliances. Near the end of the nineteenth century, the invention of dry cell batteries, which replaced the liquid electrolyte with a paste, made portable electrical devices practical.

The electrical potential difference, the terminals of a battery is known as terminal voltage and is measured in volts. The terminal voltage of a battery that is neither charging nor discharging is called the open-circuit voltage and equals the emf of the battery. Because of internal resistance, the terminal voltage of a battery that is discharging is smaller in magnitude than the open-circuit voltage and the terminal voltage of a battery that is charging exceeds the open-circuit voltage. An ideal battery has negligible internal resistance, so it would maintain a constant terminal voltage of until exhausted, then dropping to zero. If such a battery maintained 1.5 volts and stored a charge of one Coulomb then on complete discharge it would perform 1.5 Joule of work. In actual batteries, the internal resistance increases under discharge, and the open circuit voltage also decreases under discharge.

Primary batteries can produce current immediately on assembly. Disposable batteries, also called primary cells, are intended to be used once and discarded. These are most commonly used in portable devices that have low current drain, are only used intermittently, or are used well away from an alternative power source, such as in alarm and communication circuits where other electric power is only intermittently available. Disposable primary cells cannot be reliably recharged, since the chemical reactions are not easily reversible and active materials may not return to their original forms. Battery manufacturers recommend against attempting to recharge primary cells.