How to change my battery to percentage

The battery percentage level is active already and you can view your iPhone's battery level as a percentage in several ways.

Swipe down from the top right corner (ie. from the battery level bar). Percentage becomes visible as the text and icons move down.

Add the battery widget to the Today View and you can swipe right at the lock screen or from the first page of apps if the phone is open: edit the home screen, tap on the + icon at the top left then select the battery icon.

You can ask Siri to speak the battery level.

CSTidwell Said:

"How to change my battery percentage"

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Get a New Battery:

Do you mean the Battery Health? If so, you can't. So get a new battery. Important: Have Apple or an AASP (Apple Authorized Service Provider) perform it, elsewise you may get scammed with a ungenuine battery.