Updating iOS 16.6 on IPhone 11 reduce my battery health faster.

Loss of battery capacity is not linear. Although, on average, a battery loses about 1% capacity a month, that's just an average. And, the indicator isn't always accurate. When you update the phone, it recalibrates the battery health number.

If you have the original battery in your iPhone 11, it's certainly getting on toward the end of its life. But, there may also be something wrong with it. I suggest that you contact Apple and arrange to have it evaluated. They can do some diagnostics remotely.

Genius Bar Reservation and Apple Support Options - Apple

The_pantastic Said:

"Updating iOS 16.6 on IPhone 11 reduce my battery health faster.: I’ve notice that, after I update my iOS to 16.6 my battery health goes down much faster compare to my previous software which 16.5 and it’s been 4 weeks after I update it and I already lose 6% on my battery health from 92% - 86%.[...]"

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Troubleshooting Battery Issues After an iOS Update:

Unfortunately, there is no way to determine why, nor when the downgrade occurred. The update may or may not caused this. So, report it to Apple.

Report this to Apple:

Do your Part: Provide Apple with feedback on this, letting them know what exactly is occurring.  Apple may not get back to you directly, but the more feedback they receive on this, the more they will know what is occurring, and what bug fixes to include in updates to come. They will know nothing of this, if it is not reported to them.

1. Go Here: Feedback - iPhone - Apple
2. Select: "Bug Report" for the "Feedback Type"
3. Comment: that this all occurred after installing an update, and how you have troubleshot it thus far. Include the URL of this thread.
4. Proceed from there as necessary

there has been multiply problems like this in the past most have been solved by limiting the amount of apps and storage plus data you use also Maby if it goes far enough getting a upgrade to a better phone because the 11 is getting old