eli5 how do batteries get more charge when you leave them for awhile?

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eli5 how do batteries get more charge when you leave them for awhile?

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The post didn’t specify the type of device and battery in question, different types work in different ways

Phones for example measure the battery voltage and calculate the charge level based on it when they start up. After that, instead of measuring constantly, they measure the phone’s power draw and calculate battery charge level based on that.

This means that the calculated value is not 100% accurate. It’s better to undershoot and show less charge than there actually is, because then the user won’t have the experience of having 10% left one moment, phone shutting off a second later. Because undershooting is better from the user’s perspective, they calibrate the calculations to do that. When you turn the phone off and back on, it does the measurement again, so the moment it turns on, the undershoot is corrected.

One more reason to undershoot is because fully discharging a battery can damage it, so it’s safer to shut the phone off at a higher charge

When a battery discharges, liquid or gelled chemicals in the battery react with metal foil in order to release electrons. If the battery is heavily drained, the chemicals closest to the metals surfaces are depleted. When the battery rests, chemicals farther away can migrate closer to the metal, and release another burst of energy later.

It is slightly more complicated, and some batteries don’t use the metals themselves, but substances coated onto metals, but the principle is the same. Warming a battery will also help you eke out more energy from it, as this makes the chemicals move easier. If you decide to try this, don’t ever get a battery wet or more than lukewarm, some may explode or ignite.