New iPhone 13 battery health is showing 98%

You should expect Battery Health to decline about 1% a month over the first year. Your battery is doing fine. It might really be at 98.9%, but that will display as 98%.

Make that you have Optimized Battery Charging enabled and that you are plugging the phone into the charger overnight, every night.

There is nothing wrong with your battery. It is normal to drop about 1% per month based on the use of the phone. Only worry when it gets to 80% or less. Then get a new battery.

but some of my friend have 13 too but they have it for half year and 100% battery

Your friends are lucky. My wife's iPhone and my iPhone are 5 months old and the battery is at 94%. This is normal.

Apple will not help you or replace the battery unless it is below 80%.

Charging the phone overnight every night is the best thing that you can do to help the battery. Please stop worrying about the battery. Things are normal.

There is nothing wrong with your battery. If you don't believe that, take the iPhone to an Apple Store. But, be prepared for them to tell you that there is nothing wrong with your battery.

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Connect the phone to the charger every night before you go to bed and let it charge overnight.