Why does my iPhone turns off by itself
My iPhone turns off while I’m using it by itself
iPhone 11, iOS 17
Question marked as
It could be that your battery has reached the end of it's life.
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. This is an approximation, that is why it may be plus or minus a few percent on a month to month basis.
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)