Today's power tool batteries owe their basic design and operating characteristics to a pair of 18th century Italian engineers and a trio of 19th century French scientists. They laid the groundwork for cadmium-lithium, nickel-metal hydride and other portable cell technology that most people now take for granted.

Luigi Galvani (1737-1798) conducted a series of experiments on "animal electricity." He applied current to the nerves of a frog and observed the contractions of the muscles in its legs. Among other things, Galvani discovered that when connected pieces of iron and brass were applied to frog's legs, they caused them to twitch.

He speculated that electricity was stored in the leg, a theory that attracted a widespread following but was later proven wrong. The words "galvanic," "galvanize" and "galvanometer" are named after him.

Alessandro Volta (1745-1827) experimented primarily with static electricity until he heard of Galvani's observations. He was convinced that the presence of two metals was all that mattered, so he began experimenting with copper, silver, tin and zinc plates and rings. He used cardboard soaked in vinegar and U-shaped metal strips to produce electric currents.

In 1800, Volta stacked a series of alternating metal rings to form a pile, resulting in the world's first dry battery. The column battery or voltaic pile was the first device to produce electrical energy that could continuously flow down a wire.

The words "volt, "voltage" and "voltaic" are named after Volta. In 1881, the International Electrical Congress in Paris established the volt as the standard unit for measuring electrical pressure and electromotive force.

French scientists in the 19th century picked up where Galvani and Volta left off. The next important step in the evolution of electrical energy storage was the invention of the lead acid battery in 1859 by French physicist Gaston Plante. His chemical battery used a liquid electrolyte. The battery was made by rolling thin strips of lead foil, with porous insulating material between them, into a jelly roll shape. The cylindrical cell was submersed in dilute sulfuric acid electrolyte. Plante's battery was first used to keep the lights on in railway carriages while stopped at train stations.

Plante's countryman, Georges Leclanche (1839-1882), invented the dry-cell battery in the 1868. He used a damp paste electrolyte so there was no liquid to leak out.

In 1881, a third Frenchman, Camille Faure, invented a version of the lead-acid battery that substituted a flat lead grid structure in place of lead foil. These grids were cast as a flat lattice, into which a lead oxide paste was pressed, forming a plate. The plates were stacked to obtain the desired performance. This assembly method made is easy to mass-produce the battery.