My iPhone don’t add percentages once it reaches 80 percent
What is the fault that happened to the iPhone that make it not add percent once it reaches 80 percent
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It sounds like Optimized Battery Charging is enabled. Your iPhone charges to 80%, and waits to fully charge until it expects you to use it. This is done to protect the battery from wear and tear. The function is enabled by default.
You can disable the feature here:
Settings → Battery > Battery Health & Charging → disable Optimized Battery Charging.
You can read more about the function here:
About Optimized Battery Charging on your iPhone - Apple Support