If I leave it off, it records my sleep/constant sp02 just fine. When I had it on /enabled (battery protection) for the first week of of owning the phone the sleep section failed, the watch simply displayed the default "wear your watch the analyse sleep patterns" message or something along those lines (the standard opening screen of the sleep tile when no record has been recorded).
It worked (the watch/SS health etc) flawlessly when it was hooked up to my old device, (s8+) but as that phone didn't have the battery protection feature I decided to try it with it disabled and it recorded the following night's sleep just fine and blood oxygen, too be honest though snore detection is still a bit hit and miss.
My old device had 100 records history ready to show the sleep apnea clinic when my appointment comes through but I've only managed to get her 2 or 3 records since owning this phone.
I would like to have battery protection enabled as I've had it turned on since I've owned my tablet, it does behave differently on my tablet though as in it still displays the battery as 100% full when charged, on my s21 Fe though it actually stops at 85%.
I opened a question/error ticket but it hasn't been answered yet. So I've simply disabled the option (b-protection) for now.
