Battery health

Perhaps this article will help:

iPhone Battery and Performance - Apple Support

How long have you had it? It's one of those odd things that the battery health isn't a "real time" reading. I've seen it drop in chunks where it seemed like it never changed for months at time and then 3-5% drop almost overnight. It seems to save up and then catches up. Not sure why, but if 89% is in line with how long you've had it and used the battery, there isn't really anything to be alarmed about. It won't actually lose 9% battery health in a month.

arsen37 Said:

"Battery health: Hi ! I have a problem wirh my iphone 11 pro max, the health of phone was 98%, during a month it became 89% percent. What can I do?"

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You're Fine. Wait until it gets to 80%. Apple recommends that you get a new battery when the Battery Health reaches 80%. Unfortunately there is no way of knowing why this occurred and when. But, all batteries are prone to failure.

arsen37 wrote:

I had the phone for 2 years, but the problem became month ago, or I paid attention to it. Last week it was 90% , yesterday became 89

It doesn't really sound like anything all that alarming. I get that it sounds odd for the number to drop that quickly, but it's pretty odd for it to stay at such a high value for so long. That's just kind of the way it works sometimes. But 89% after 2 years is better than Apple's rating if a linear decline in battery health is assumed with an average of 25 cycles a month.

There are also a lot of little variables that go into battery decline. But it's all packed into a one-size fits all longevity rating of 500 cycles to 80% battery health.

That's not a problem, 89% for a 2 year old phone is actually quite good.

Yes, current flow will do that.