Him Zafi-80,
You did well by waiting for a few days after the update, as there can be some background updating happening which can't be avoided. However, there is background activity which you can try to avoid.
Updating your apps after an iOS update. Many app developers will release their updates when the iOS is updated, which can download and install in the background. Here's what you can do to help avoid this situation:
1. After updating your iPhone, while you're still connected to power and Wi-Fi, is to check if you have any app updates to download or install.
2. Follow these steps: How to manually update apps on your Apple device - Apple Support
3. Then, while you're on the update screen, swipe down to refresh, as you may see more available.
4. Keep plugged into power until all app updates are completed.
5. Check again in a day or so, just to verify if any new ones were released.
If your apps are all up to date, and you're still having battery life issues, you'll want to check the health of your battery.
Settings > Battery > Battery Health & Charging > Maximum Capacity.
If that is below 80%, it's time for a new battery, as shown here:
Batteries - Service and Recycling - Apple
More info on battery performance: iPhone Battery and Performance - Apple Support
Take care!
