Hello.
First time writing here, but I wanted to give my input.
I am not an expert in battery issues on Android, but I always check the status of the battery through the /sys directory.
You will find all battery related information accessible under /sys/class/power_supply/battery. This is the folder that all apps use to either read or set battery related issues or settings.
Both the structure and file names have been changing over the last versions of Android, so I can only tell you what I am able to see on my Samsung Galaxy S7 Edge. You might find it easier to use an app to do this for you, but I always do it manually and can't therefore recommend any.
I recommend checking out /sys/class/power_supply/battery/fg_fullcapnom with a text editor. I just use Solid Explorer and it's text editor. This file should show you how many mA are left of your battery. Personally I would fully charge both S9 phones and compare those numbers to see if there is a difference. If your phone is often warm, then that tends to degrade your battery, so this would be a good place to compare. When the phone shows 100%, it will show that as relative to the current maximum capacity instead of the original maximum capacity.
Of course, you did note in the video that you did not see this happening while you were using it, but I think sharing the comparison of the capacity numbers would aid with the discussion here, especially because most people here are recommending replacing the battery or swapping it between phones.
Best wishes
Frey Alfredsson
