How is you battery doing now? I posted on the m1 issues thread about my MBP M1 battery drain when running an external monitor (or even just the USB-C hub). When running an external display or USB hub my YouTube playback per 1% battery dropped from 12 minutes to 5-6 minutes. I contacted Apple support, it was escalated to senior support and some engineers took logs from my computer, but nothing out the ordinary was found. Just advised that peripheries can run the power down, even whilst asleep (which it did). As I was in the 14 day return window he said I could get it replaced, however it would likely behave the same. When nothing is plugged in, the battery is excellent. Now I just leave it plugged in normally as support advised.