so I have a 2019 MacBook Pro 16" on Catalina 10.15.5. I recently got it back from the shop - upper case replacement for bad keyboard that included replacing the battery as part of the repair. Now I've noticed that while its plugged in and 100% charge and I'm using it, the battery charge actually decreases. For instance last night I opened it, it was plugged in at 100%. I used it to make an email and print a few pages for 15 minutes and the charge actually decreased to 93%. The icon shows when plugged in.
I have looked at MacBook Pro battery drains when connected to AC power but Battery Health Management is not turned on so it seems to be something else in my case.
How can I diagnose and solve this issue?
PS: I'm using an OEM 96W power adapter.