Garmins easily last a week.
Overnight camping, and sleeping in a tent for a few nights is a good example. I'm not "taking a shower" and hence don't really have a great time to charge it. With my garmin I just leave it on, and it keeps working for the entire trip.
Same thing with other "adventure" travel, flying overnight, etc.
Funny as I bought it as they advertised sleep measurement features. I quickly realized I need to actively think about charging time and at some point I just stopped using it.
I generally put it on the charger every evening around 7 pm or so when I sit on the couch to do the NYT crossword and Sudoku (which come out at 7 pm in my time zone) and watch some TV or read for a while.
It then goes back on my wrist but in theater mode and with notifications silenced until morning.
It generally uses maybe 5-10% while I sleep. In the morning I turn theater mode off and un-silence notifications, and then use it to track 30-35 minutes of exercise.
It is typically still above 30% when it is time to do the next crossword.
You have to micromanage the thing. It does not just work. You have to constantly adapt strategies depending on usage pattern and lifestyle change.
I do not use smartwatch features (basically useless or worse an intrusion/interruption in your life for little benefits).
People seem to think Apple Watches are good. As an owner for 6 years or different generations, I beg to disagree.
The only thing it's good for is the quality of the data but competitors have caught up and it's not that important (consistency of measurement is more relevant). What's more when you can't use it because of battery issues it becomes moot; a bit worse data is still better than no data at all in the end.
In my opinion the Apple Watch is the perfect representation of Apple lack of focus and inability to make relevant compromise to create actually great products.
They could make a killer sport watch with low refresh rate on the display, minimum power consumption with a chip that would only run the data collection and forgo all the app bullshit to get something that could potentially last up to a week.
But they would rather sell lifestyle fashion accessories.