The battery
A chemical reaction that wants to happen, not stored electricity.
A battery holds no electricity: it holds a chemical reaction that wants to happen. It is a flat cell, rolled or folded inside a soft pouch, which pushes electrons with a voltage of about 3.6 V, a little more when full, 4.2 V. Its capacity is counted in milliampere-hours: a recent phone's is for instance 4,200 mAh, which is how many charges it can push through before the urge is spent. When you wake the screen, that urge is what works, and the gauge drops. "Empty" does not mean nothing is left inside: the reaction has simply run its course. To understand where the push comes from, you have to go inside the cell.
Sources
- ≈ 3.6 V BU-303: Confusion with Voltages, Battery University, retrieved 11 October 2026.
- 4.2 V BU-303: Confusion with Voltages, Battery University, retrieved 11 October 2026.
- 4,200 mAh Fairphone 5 Battery — Spare Part, Fairphone, retrieved 11 October 2026.