My iPhone battery health dropped by 1% on the first day of use

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.

iPhone Battery Repair & Replacement - Apple Support

About Lithium Ion Batteries

iPhone Battery and Performance - Apple Support (IN)

Here are some tips on maximizing battery life.

Batteries - Maximizing Performance - Apple Batteries - Maximizing Performance - Apple

Adhikarikiran Said:

"Battery health: wath problem my iPhone battery health drop 1 day 1% ?"

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Battery Health Decline:

Unfortunately, there is no way to determine why, nor when, the Battery Health declined.

Troubleshooting iPhone Charge:

Visit the following links for tips on troubleshooting this...

I. Try what is on this Link: If your iPhone, iPad, or iPod touch won't Turn on or is Frozen - Apple Support

II. View the Battery Health:

Apple recommends you get a new battery, once the Battery Health reaches 80% or lower. When the Battery Health is 80% or lower, it is time for a new battery.

1. Go To: Settings
2. Tap: Battery
3. Tap: Battery Health
4. View: [the percentage]
5. Is it 80% or less?  If so, it is time for a new battery.

III. Perform a Restart:

Try Force Restarting your iPhone. Save any information that need be. Then perform the restart.

Go Here: Force Restart iPhone - Apple Support

IV. A Few Apple Support Sites that May Help:

• iPhone Battery and Performance - Apple Support

• Charge and Monitor the iPhone Battery - Apple Support

• About the Battery Usage on your iPhone - Apple Support

• If your iPhone or iPod touch won't Charge -Apple Support

• About Optimized Battery Charging on your iPhone - Apple Support

• If you see "Your iPhone Battery may Need to be Serviced" - Apple Support