ELI5, how do devices that use batteries, like phones, know the percentage of the charge remaining?

Question

ELI5, how do devices that use batteries, like phones, know the percentage of the charge remaining?

In: Technology

Answer 1

They measure the voltage. Think of batteries as tubes of angry pixies. Voltage is just how angry the pixies are. The more voltage, the angrier the pixies are. When the pixies get tired, the voltage drops. When the pixies get all tuckered out, the battery is dead.

Every battery has a known voltage when full. The device either computes a ratio to flat dead, or to “low enough” that the pixies can’t do any work for the device