MBP (13-inch; M1; 2020) battery performance

I updated the OS out-of-the-box so I have no idea how the battery performed under the factory-installed OS. What I have noticed is that battery drain is rather significant with little to no activity. In essence, the machine is on with 2 external USB drives attached. But otherwise sees little significant usage. Over the past 2 weeks, I've left the MBP plugged into the power adapter - only to learn the battery has reached 78%, down from 100%.

Energy Usage report for the past 7 days shows (1 day @ 25%, 4 days 0%, 2 days 1%). All while being plugged into the Power Adapter. I figured that being plugged in, there wouldn't be much drain on the battery - that's certainly how my older MBP behaved.

On a slightly different note - the machine has AppleCare+ through 2024, the machine shows that information (as well as the support app on my iPhone and iPad) - but when I visit Apple's support site it claims that it can't find AppleCare information for the subject MBP. That, after clicking the Get Support... link from the Support Tab of About the Machine panel on the device in question.

I probably wouldn't think much of it - but there seems to be something not quite right with the MBP.

[Re-Titled by Moderator]