Batary Health

Batteries degrade over time with usage, 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

Here are some tips on maximizing battery life.

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

is there any possibility to make it 100%?

No, unless you replace the battery.