Recently my note 9 will do fine above 20% in battery but, whenever it reaches 20% or below in charge it drains within minutes. Then whenever it reaches 7-13% it dies without reaching 0%. It happens everytime my reaches 20%, no matter what app I use.
Thanks for reaching out. Have you optimized your battery recently? Try testing your device in safe mode to see if the same symptoms still occur, Third-party apps running in the background can cause major battery drainage.
To boot your phone into Safe mode, start by pressing and holding the power button until the power menu appears on your screen. From there, long-press the "Power Off" button until it turns into a "Safe Mode" button. Simply tap on "Safe Mode" once it appears and your device will automatically reboot to safe mode.
I would recommend doing what was suggested below, by putting your phone into safe mode and seeing if this battery drain continues, but also take a look at what apps are using battery.
If you go to 'settings' 'device care', and click on 'battery', then 'battery usage' it will show you a breakdown (highest to lowest) of what applications are using your battery.
If this shows an app that is clearly using a lot of battery try removing it as it might be bugged out.
I would recommend taking a look at the battery usage before putting your phone into safe mode to get an idea of what the issue may be.