Same here. My MacBook Pro 15” (2015), would last about 2.5 hours connected to my Thunderbolt Display as I worked. After updating to macOS Big Sur, I noticed that the battery was draining really fast and decided to use my timer to track how long it would last with a full-charge. Within an 1hr & 26mins my battery was at 16%. It took 4 HOURS to recharge. I then tested to see how long it would last without the Thunderbolt Display, and just one chrome window open with a YouTube video running. The battery went down to 30% by 1hr. it’s like a flashback to when people called them out for purposely making older iPhones run slower, and run out of battery faster with the latest iOS updates.