Phone will not stay on unless it’s plugged into a charger
Why won’t my iPhone stay on unless it’s plugged into a charger
iPhone 8, iOS 16
Question marked as
Your battery is most likely dead.
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.
https://support.apple.com/iphone/repair/service/battery-power
About Lithium Ion Batteries
https://support.apple.com/en-in/HT208387