After last update to 21.0 my battery is drain 50 % per day.So I rolled back to firmware v. 20 and everything it back to normal .
If someone won't to roll back download firmware Fenix5_20.72beta inside is folder System_backdate2000.
From that folder copy file GUPDATE.GCD in main folder of your Fenix 5 watch ,after that disconnect watch from computer.
Follow on screen of watch instructions