Battery Charge & Coulomb Converter

The story of measured electric charge starts with Charles François de Cisternay du Fay, a French chemist who in 1733 noticed that there are two distinct kinds of electricity. Rubbed amber and rubbed glass repel objects of their own kind but attract each other. He named them resinous and vitreous and gave us the first two-fluid theory of electricity.

In the 1740s Benjamin Franklin replaced du Fay's two-fluid model with a single-fluid theory: too much fluid is positive, too little is negative. Franklin guessed wrong about which way the fluid flowed, but his arbitrary sign convention has survived nearly three hundred years - the reason current today flows from + to − even though electrons drift the other way.

The quantitative breakthrough came in 1785 when Charles-Augustin de Coulomb published his torsion-balance experiments. By twisting a fine silver wire suspended between two charged spheres he showed that electrical force, like gravity, obeys an inverse-square law. The Académie des Sciences had him present the work in three memoirs that year. The SI unit of charge bears his name, named at the 1881 Paris International Electrical Congress alongside the volt and the ohm.

Michael Faraday turned charge from a force into a current of substance. His 1834 laws of electrolysis showed that the mass of metal deposited at an electrode is proportional to the charge passed through the electrolyte, and that the proportionality is set by the metal's equivalent weight. The constant linking moles and coulombs - 96 485.33 C/mol - became the Faraday constant, the first hint that electricity itself is built from countable, identical bits.

That hint became proof in 1909 at the University of Chicago, where Robert Millikan and Harvey Fletcher sprayed atomised oil through a charging zone and into the gap between two parallel plates. By adjusting the voltage they could float a single droplet while it lost and gained charge. Every measured value was an integer multiple of a single fundamental quantity: 1.59 × 10⁻¹⁹ C, less than 1% from the modern exact value. Millikan was awarded the 1923 Nobel Prize in Physics for the experiment.

For most of the twentieth century the coulomb remained defined indirectly through the ampere: the current that produces a fixed force between two parallel wires. This was awkward in practice and impossible at the level of single electrons. The 26th General Conference on Weights and Measures fixed the situation on 20 May 2019 by redefining the elementary charge as exactly 1.602176634 × 10⁻¹⁹ C - no uncertainty - and using it together with fixed values of the Planck constant, the Boltzmann constant, and the Avogadro constant to define the ampere, the volt, the ohm, and every other electrical unit.

Today metrologists count single electrons with single-electron transistors and Coulomb-blockade pumps, watching exactly N electrons flow through a tiny nano-channel per second. The current is then exactly N × e amperes. The unit that began as a man's name attached to a torsion balance now lives in cryostats, traceable to the atomic constants of the universe. The tool above keeps the same chain of mathematics: every input - whether a phone battery, a copper-electrolysis vat, or a counted electron - maps to coulombs, runs through IEEE 754 double precision, and lands on the unit you actually use.