Download this app:
https://forums.androidcentral.com/e...?id=com.gombosdev.ampere&hl=en&token=zP006pyS
Check out the maximum current that your phone can use while charging. Know this googling "your device name" + "maximum charging current"
It will be shown in mAh units. In my phone it is 1000 mAh.
Now, connect your phone to the charger and launch the Ampere app. Note that the reading in the home screen. If it is equal to your phone's default current and remains stable, your phone is good. The battery is dying or maybe the OS is buggy. If the reading in the app is less or reduces constantly, your charger, USB cable or USB charging port is damaged.
Because you specifically mentioned that you have updated the OS, there can be high chances that the OS isn't yet fully compatible or it's highly buggy. Having found the main source to your problem, I recommend you to do one or more of the following, as applicable:
1. Change your downgrade your OS
2.Change your USB cable
3. Change your charger
4.Don't charge your phone with a PC, TV, powerbanks or cheap or local cables and chargers or any other source except from your orginal charger.
5.Replace your battery
6.Stop disturbing it while it's charging.