Same issue here, MacBook Pro 13 inch, 2020. First I thought it was because of some app I recently installed, but now I realize the problem is with Big Sur. It's almost useless as a portable computer in this condition - 3 hours of word-processing drains the battery to about 35%, then after another 30 minutes I have to shut it down. The computer gets extremely hot (as was never the case before the upgrade). A fix is needed quickly.....