My iphone 7plus lots it’s charge once.
My iPhone suddenly lost its charge quickly and turned off, when I put it back on the charger, it charged slowly
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Your battery may be at the end of its 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)