Sudden rapid battery drain (vivoactive 4s)

My watch has been running fine for 5+ years, the battery has gradually deteriorated (which is fine) and lately I have been getting about 3 days on a charge... until this week. On Monday I switched to a novelty watch face, just for fun. It's a watch face I've used before with no issues. I did expect it to drain the battery a bit faster, which it did - I went from a full charge to 20% in a single day - so I switched back. Despite switching back to my normal watch face, the battery drain has persisted!

I have tried everything I could think of or find on the Garmin forums as fixes:

  • switched back to the previous watch face
  • uninstalled the problem watch face
  • uninstalled all 3rd party watch faces
  • reviewed my settings, lowered the brightness, lowered the vibration intensity
  • cleaned the sensors
  • updated the software
  • factory reset
  • factory reset and erase all data

NONE of this has restored my battery usage to the previous "a charge lasts 3 days." (I didn't turn off Bluetooth because it was never a problem before and that destroys a lot of the functionality of the watch.) If anything, it has gotten worse - on Friday and yesterday it was draining about 4% per hour; today (after the second factory reset) it is draining TWENTY PERCENT AN HOUR.

Have I bricked my watch? This sucks! I don't want a new watch! Changing the watch face shouldn't have permanent effects!

What can I do to fix this?