You should test your battery on Windows to verify.
So, under Windows has the same problem. I used powercfg /batteryreport to see the capacity before and after AC plug/unplug and has the same behavior as macOS. So my new battery is defective. It will be replaced under warranty after 14 days because they don't have the battery on stock.
Sorry for spaming the forum with posts when my problem was a hardware problem.
Nice to hear you have determine the source of the problem.
Goes to show: Must test your assumptions regarding hardware function on Windows before assuming there is some software problem!