The phone was charged for a long time. Why quickly discharged?

Question

Mobile devices

I searched on the Internet and did not find the reason why when the phone lay for a long time and was not used and was fully charged at 100%, when turned on it shows a high charge of 70-80%, but after 5-10 minutes of use, just scrolling through the screen and not launching energy-intensive applications, the charge drops sharply to almost zero or 10-20%? then after a full charge of 100% this does not happen again if you regularly use the phone

Answer 1

You did not indicate the state of the battery, but according to the description it is possible that it may already be "used".
The reason is in chemistry/physics. With prolonged non-use, the voltage more or less holds, but the ability to give out the current necessary even for the screen (for modern screens you need not so small) - sags.
The situation is similar with 18650 cans. An old one can be used in a not very powerful flashlight, but in an electronic cigarette (vape) you will quickly see "Battery low", because. there are different currents.
You can read more about Lithium-ion here:

• https://batteryuniversity.com/learn/article/lithiu...
  
• https://batteryuniversity.com/learn/article/how_to...