Installed Big Sur last night on my 2020 macbook pro 15 inch. Had it at 100% charge this morning upon waking up. After taking the laptop off the power supply, my battery percentage went from 100% to 75% in a matter of seconds lol. 5 minutes later, here I am at 65% left on my laptop complaining how poorly this Big Sur OS is handling the battery and RAM. I am now receiving a "Service Recommended" for the power source: Battery. Obviously I am not going to do that, given this is a brand new laptop. Apple fix your shit.