A Battery Stores a Chemical Cliff

The drawing shows a battery as a ledge with something ready to fall, the wire drawn as the only staircase down, and a wall in the middle keeping the two sides from ever touching directly.

Before you start. You need to know that electric current is a flow of something through a wire, the way water flows through a pipe. That is the only piece of electricity this lesson assumes you already have.

The idea in 30 seconds

A battery is a height, not a bucket: it stores a difference in how hard two materials hold onto something, not a stockpile of charge.
Volta proved this by building a stack of zinc, copper and wet cardboard and getting a twitch with no frog anywhere near it - Galvani’s “animal electricity” was really just two different metals.
Voltage is the size of that drop. Capacity is how wide the drop is. A battery’s stored energy is the two multiplied together.
Bigger batteries of the same materials buy more capacity, not more voltage - an AA and a D battery of the same chemistry both say 1.5 volts.
Inside, an electron and an ion always leave the same side together, but the liquid between the two materials only lets the ion through. The electron goes the long way, through the wire, and that detour is the current your phone runs on.
That is also why it is called a lithium-ion battery: lithium is the ion taking the short way, every time.

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