Batteries degrade over time with usage due to chemical aging, that's just how they work. And the drop rate is not always linear. Your phone is 10 months old and you've dropped 9%, you're right on track.
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