Same problem here with early 2015 MBP. Big Sur killed the battery. Downgraded to Mojave, no effect. Not bothered trying upgrading to 11.2.1, since it is clear this does not fix already affected computers. Shocked to see that my model is not covered by the replacement program, despite having exactly the same issues. Spoke to support - they were no help at all - just kept saying that 'your model is not one of those affected' - total nonsense of course. At a loss of what to do next. Really disappointed by Apple. Expected more from them - really just cannot trust them to do the right thing.

Same problem. Erased HD and reverted to Catalina. No effect. Now have to setup the Mac again. Apple support continue to deny all knowledge of this despite hundreds of reports. If anyone comes up with a solution please post here.

Upgraded my 2015 MBP to Big Sur- seemed OK. Then auto updated to 11.1. Then same problem as the others on the thread. Service recommended and the battery will not charge - machine shuts down when the mains power is disconnected. Was fine before upgrade. Tried resetting SMC etc - no effect. Spoke to support - they have not heard of this issue, which was a surprise given the numerous reports I have seen. Tried to tell me that it looks a hardware issue and the battery might need to be replaced, which of course is nonsense. Suggest we all call Apple support and raise this.