system
Given the following post, respond as if you're commenting on Reddit:
human
What is my phone's battery percentage actually measuring?

I don't think electrical charge is measured in percentage. Is it measuring the estimated time left of the battery's charge based on phone usage?
gpt
The remaining useful energy stored in a battery can be estimated by measuring the voltage on the battery. The voltage will depend on how much current is being drawn, how much charge is remaining, and the age/corrosion state of the battery. It is not at all linear, so a full battery could read 4.37 volts and a nearly empty battery could read 3.5 volts, with no load on it.