How do electronics know what battery percentage they have?
In: Technology
It’s an estimate. A clever one based on lots of calculations, but it’s still an estimate.
Imagine you have a dumb battery cell, and it outputs at a voltage. Say, 5V. That’s the only thing you can measure from a battery, is what the voltage is (temperature is also measured for protection against overcharging and overheating). You run your device, and it works fine until the battery gets to 3.9V, at which point it starts misbehaving, and there’s a potential to damage the device or lose data.
So, the calculation is then done as follows:
Voltage 5V = Battery 100%
Voltage 4.5V = Battery 50%
Voltage 4V = Battery 0%
Why not 3.9V? Well, some margin is left between 4V and 3.9V for you to find a charger whilst the battery keeps things like the clock and other volatile things going. It also helps prevent against things like the phone requiring more juice than the charger can provide during start-up, so that it doesn’t flake out whilst you’re switching it on, things like that.
Basically, it’s a calibration based on trial and error. Battery calculations are also nowadays self-calibrating, which is why your laptop is able to tell you that it needs a new battery (and why Apple were fined for manipulating phones based on battery stats).
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