High battery usage

I have seen similar. In my case it was immediately after an activity but others have mentioned it can be after interaction with Garmin connect. It seems fairly spurious and I've not managed to come up with a repeatable set of steps that's guaranteed to trigger the problem.

Powering the watch down and up again (usually) halts the high battery drain. The issue is also present in current beta firmware though it's probably been around for some time. I reported it here: 

https://forums.garmin.com/beta-program/forerunner-955-series/public-beta-bug-reports/i/public-beta-version-19-xx/bug---high-battery-drain-after-run-workout

Please go there and upvote the bug report. Hopefully Garmin will track down and fix the problem!

+1, I'm seeing the same thing but non solar model.

Same here. I’ve gone from charging once a week to almost daily. Losing about  30% overnight  - Pulse Ox has always been off. No change in usage or settings - am on 18.27 955 Solar 

Same experience. Usually drain 5% daily. Noticed a 12% (90->78%) drop overnight when I woke up on 13 May. This was the 2nd unexplained sudden big drained in battery for no apparent changes in settings or updates. The first time it happen it was on older firmware. This time it happen again on 18.27.

Think i found the issue. Go heart rate chart via the app, the day there is a steep drop in battery, there is a big gap of almost 3 hours where there is no heart rate recorded. I'm wearing my watch 24/7 and should not have such gap. My hypothesis is that the watch will drain battery when it struggle to take measurements for whatever reason. Next time I observe another drop i'll take a look again at the heart rate chart. 

I’m still having same issue - but just got the new software update. Now on 19.18.  Noticed it also updated GPS and  WIFI - hoping one of these fixes the battery issue. 

One thing you might try is to clean the sensor on the back of the watch (soapy water and a soft cloth, then rinse). If it's dirty or greasy, that can cause extra battery drain, especially overnight.

Update to 19.18 made no difference at all.  Still losing up to 20% battery overnight.  Still can't bring myself to do the hard reset and lose all my watch settings (data is safe, I know).  At this point my Apple Watch battery life is on par with the Garmin.  Not something I ever thought I would say.    Been searching and reading through past battery issues to see if anything might help, but so far absolutely nothing.   So frustrating because it absolutely began with the 18.27 update. 

See if this helps with the resetting phobia :-)

Helps with the data screens anyway!

forums.garmin.com/.../some-advice-before-upgrading-replacing-a-watch-or-a-hard-reset

thanks. I've just bitten the bullet and reset.  It's not that bad, but it's those annoying settings  you never remember are set until they start annoying you half way through a workout.   Lets see if this works overnight - it will be very obvious if it has helped.