Almost everyone uses batteries every day. Almost no one I've asked outside materials science can describe, in a few sentences, what a battery actually does. This is mildly remarkable given how central they've become.
Here is the version I give to friends at dinner.
The mental model
Imagine a busy hallway between two rooms. One room is crowded with people. The other is nearly empty. People naturally want to move from the crowded room to the empty one. Open the door and they'll flow through, jostling each other as they go.
That flow — that's the current. The crowdedness difference between the two rooms — that's the voltage. And the hallway is the electrolyte: the substance that lets the people actually move.
When you discharge a battery, you're letting one side empty out into the other. When you charge it, you're pushing the people back. That's it. The chemistry varies. The model holds.
Why this model is useful
It explains why batteries lose capacity over time: each round trip wears down the doorway and the hallway. It explains why you can't pull power infinitely fast: there's only so much room in the hallway. And it explains why temperature matters: cold hallways slow everyone down.
Where the model stops
It does not explain why some chemistries dramatically outperform others. That involves real physics. But it gives you enough scaffolding that the real physics becomes legible the next time you read an article about it.
A useful model is one that's wrong in instructive ways. This one is wrong, instructively.