Battery

Batteries degrade over time with usage due to chemical aging, that's just how they work.

You can expect about a 1% drop per month with average use on an iPhone.

Apple recommends replacing it when it reaches 80%. To check your battery health, go to Settings > Battery > Battery Health.

iPhone Battery Replacement.

iPhone Battery Repair & Replacement - Apple Support

About Lithium Ion Batteries

iPhone Battery and Performance - Apple Support (IN)

Here are some tips on maximizing battery life.

Batteries - Maximizing Performance - Apple

Starthefemboy Said:

"Battery: Why is my battery health at 88% after 9 months of use I had a old iPhone 7 that battery health didn’t drain that fast I’m on iPhone 11 is thing a thing that happens with these new phone or should I be concerned"

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Why the Battery health Decreased:

Unfortunately, there is no way to determine why, nor when, the Battery Health decreases. There is nothing to worry about.