As stated in the title, my 2019 16-inch MacBook Pro has been self-discharging continuously ever since I updated to macOS 10.15.8.
By continuously, I mean all the time. It discharges when plugged-in (I am using the original cable and charger which are in good shape), and it also discharges while it is completely turned off (not in sleep-mode, off). The laptop is pluggged-in most of the time I use it but I need to rely on its battery for work-related field activities.
I bought this computer in 2020 and have happily been using it ever since under Catalina (10.15.4 I believe). I have performed a clean install at every Catalina "upgrade" just to keep things as clean as possible. I have never needed to update to newer macOS versions because I use it for work and have never had any use for the more recent macOS versions. I mostly do scientific computing on it (Mathematica, Python and LaTeX for documents); other than that, I use the Mail, Messages and Facetime apps. I use internet through Firefox, but it is not my main activity on it.
I cannot remember the exact numbers, but prior to the 10.15.8 update, battery capacity was at 92%, with around 200 cycles. Ever since the update (around a month ago) I started noticing that the current charge was around 95% percent every time I turned it on (after plugging it in).
This means that the computer is self-discharging while being completely off. However, I was not alarmed about this at first because I initially thought that I was perhaps doing something wrong. Now I am practically sure that not only the laptop is self-discharging itself all the time, but it is also losing capacity, practically in real-time under my nose.
I have installed "Coconut" just yesterday after finally realizing that something is wrong after all. The following 3 screen-shots span around 1 hour of use this morning. They illustrate that the computer is self-discharging while plugged-in. The last screen shows a 0.1% capacity loss in less than 24 hours.
I cannot understand how the battery lost less than 10% in six years of intensive use and suddenly more than 5% in just weeks. Is there a way I can access the battery usage history to confirm that the battery is self-discharging while completely off?
My guess is that the new firmware messed things up (the current version on it is Boot ROM Version: 2103.100.6.0.0 (iBridge: 23.16.14242.0.0,0)). Is there a way to revert this firmware to a previous one? (I have been told that a clean install of 10.15.7 would not downgrade the firmware).
Update: I forgot to mention that this computer has always operated without the battery health management option available since 10.5.5.
