Why does a laptop say it’s at 6-8% charge, and then it dies, but when it’s at a higher charge, going from 60% to 59% takes a while?
In: Technology
Because it’s an estimation. The computer doesn’t actually know how much charge is left. Batteries are direct current, that means as the battery discharges the output voltage changes. Through battery testing they’re able to determine a reproducible voltage curve. Then they assign percentage of charge to voltage. By measuring the voltage the computer can estimate the amount of charge left.
As the battery ages the chemistry changes making the voltage curve not as predictable as programmed. That’s why the battery will die at 6%. Then when you plug it in it says 0%.
Voltage curve:
https://images.app.goo.gl/aws4HdaGGfThUhYBA
In the image it starts at 1.5 V then gradually decreases to 1 V then suddenly goes to zero.
When rechargeable batteries age the sudden drop in voltage drifts to the left due to changes in the battery chemistry. So instead of suddenly dropping to zero at one volt it’ll do it at 1.2 volts. The computer thinks 1.2 V is 6%, so it says 6% battery life left. Then the sudden drop occurs and the battery dies.
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