About 1.5 - 2 years ago I went from about 5 days on a charge (Forerunner 945) to just over 2 days after a software update (I didn't catch it initially). Pretty frustrating and I tried all the workarounds and could not restore my previous battery life.
4-5 days ago my watch did another update (version 11.60 (19e1fb5) and the battery life seems to be back to normal. I am at 60% with last charge 3.5 days ago. No change in settings by me since then. Thank you Garmin for finally fixing this issue (without acknowledging it...).