Battery

In 1800 Alessandro Volta stacks discs of zinc and copper, separated by brine-soaked cardboard, and gets a steady current. That pile is the first battery. Static electricity was already a parlor trick. A battery is current you can leave on.

The contribution is a circuit that does not depend on a thunderstorm or a spinning magnet. Telegraph experiments, electroplating, and the study of electromagnetism all sit on this. Faraday's motor and generator come a generation later, once people have a current to work with.

A battery stores chemical energy and gives it back as electricity. It does not create energy. That limit is why phones and humanoid robots are still gated by how much charge a small cell can hold.

Volta's pile is bulky and weak by modern standards. The idea, two metals and an electrolyte, is still how a battery works.