The correct way to calibrate your phone battery manually without using apps and make it last longer.

First: Identifying the Cause of the Problem
If your phone’s battery is removable, turn off the phone, remove the battery and inspect it. If you notice swelling or leakage, as shown in the image, you should buy a new battery as the problem lies with the battery. Do not attempt to open a swollen battery as it may explode. If the battery is in good condition, we recommend calibrating it as follows:
Understanding Battery Calibration
Android has a feature called “BatteryStats” which tracks the battery’s performance, but it may provide incorrect information to the software, leading to premature shutdown. Battery calibration corrects this information
Second: How to Calibrate the Phone’s Battery
1- Fully drain your phone’s battery until it shuts off automatically.
2- Turn it back on and let it shut off automatically to remove all charge in the battery.
3- Charge the phone while it is off until it reaches 100%
4- Turn on the phone, and if it does not show 100% charged, charge it while it is on until it reaches 100%.
5- Remove the phone from the charger, then turn it on. If it does not show 100%, charge it again until it shows 100%.
6- Repeat the above steps until you see the 100% mark without the phone being connected to the charger.
7- Allow the battery to completely drain and the phone to shut off again.
8- Recharge the phone without interruption until it reaches 100%
By following these steps, you have successfully calibrated the battery on the Android operating system, and the issue should be resolved.
Source ifixit
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By: Al Baha