My Bangle JS2 battery has gone 37 days and is at 9% now

I estimate that I'm typically getting up to around 2 weeks regularly wearing the watch with:

• a clock that updates once a minute
  
• health monitoring set to every 10 minutes
  
• wake-on-twist/motion and so on disabled (despite trying all sorts of settings I never could get them to work well without constant false wake-ups anyway)
  
• some occasional timer/stopwatch/alarm use
  
• not really any GPS use (due to lack of need and because of the relatively severe limitations)
  
  

which seems pretty reasonable. In practice since I use the watch as a daily driver I normally charge a bit more often than that to avoid the battery dying at a bad moment. Since the battery meter tends to hang out around 9–10% for a long time it's hard to be sure what the true max runtime would be without risking that; I consider that level as a sort of “charge as soon as possible” low-battery signal.

I do notice that long use of timers that update in 0.1-second intervals tend to drain the battery particularly rapidly. (At least one app seems to do such updates only when the screen is awake/unlocked and then cuts back to once per second, which seems like a good idea.) But occasional use of once-per-second displays for a few hours here and there doesn't seem to hurt overall runtime too badly.