Battery problem

Apple recommends installing a new battery when Battery Health reaches 80%. Yours is close enough to that figure so you should make an appointment at the nearest Apple Store for Battery Replacement. The typical Apple Battery lasts for about 2 years of normal use, so yours is living on borrowed time. Check this link...

Apple Store - Find a Store - Apple

Or this one...

iPhone Battery Repair & Replacement - Apple Support

Open Settings ➢ Battery ➢ Battery Health.

If the battery is 80% or less, then it’s time to replace the battery.

iPhone Battery Replacement:

Current Apple Prices:

• No charge for in-warranty or AppleCare+ plan.

Out of Warranty Prices:

• iPhone X or newer: $69 U.S. Dollars.
• Older models: $49 U.S. Dollars.

➢ Check AppleCare Coverage.

Click ▶︎ iPhone Battery Replacement.

Tuntrex09 Said:

"Battery problem: Battery problem reduce every day from 100% to 81% pls"

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Thank you for the screenshot.

When it's Time for a New Battery:

If it keeps going down, then it will reach 80% pretty soon. Once the percentage reaches 80%, that is when Apple recommends you get a new battery.

Why the Issue?

Unfortunately,, there is no way to know why, nor when, Battery Health percentage decrease occurs. You just have to wait for it to happen. All batteries are prone to failure (eventually corrosion).