iPhone Battery indicator freezing at single value and randomly dropping

[humpbacktwale]

When I go from wifi to mobile, the battery indicator will freeze at the current percentage for upwards to 10 hours. After switching mobile data off, or turning it off and going back to wifi, it will drop down by usually 5-10% in the space of an hour. No usage to indicate why this occurs, and sometimes it doesn't happen at all. Has anyone else experienced a similar issue? I can't seem to find a cause for it, and I have already had Apple run a diagnostic, and they couldn't find any issue with my battery.

It's also turned off when the battery was low, generally <20%, but still not at 0%. I am wondering if maybe the value it's displaying isn't accurate, or at least the drop may be to compensate for the random freezing?

 

[CoronaOnTap]

What’s the battery health listed as?
These are usually the symptoms of bad calibration which can be mitigated by draining it all the way down till it shuts off and then charging it all the way back up to 100% while not using if you could.

 

[humpbacktwale]

97%. Already had apple look into that as a possibility. Already tried that multiple times. Doesn't seem to have mitigated the issue.
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Mostly I am curious to see if anyone else has experienced a similar issue, so that I can be sure this is just a bug of some sort.

 

[CoronaOnTap]

Then it’s most likely a messed up battery.

My 6s did the same thing last year and the battery health was at 97%. But just merely updating the apps from a fresh start would drain the battery every 2 seconds, yes I said seconds. The Apple diagnostics came out okay but I insisted they change the battery and that I wasn’t paying for it. They declined!
I left a scathing feedback about my experience with the Genius Bar associate. Got a call from the manager the next day offering a courtesy replacement as he noticed some unusual battery behavior. All was good for a few months.