Hi there Verm69,
If the battery of your iPhone is not lasting as long as expected, the first thing we would recommend is ensuring your iPhone is fully updated. This installs security updates and bug fixes that can resolve behavior like this. These steps from Update your iPhone or iPad show how:
1. Back up your device using iCloud or your computer.
2. Plug your device into power and connect to the internet with Wi-Fi.
3. Go to Settings > General, then tap Software Update.
4. Choose the software update that you want to install. You can choose to stay on iOS or iPadOS 15 and still get important security updates. Or you can choose the option to upgrade to iOS or iPadOS 16.
5. Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do.
Once the iPhone is fully updated, also make sure that your settings are adjusted so that you’re getting the maximum life out of your battery. There are some great tips for that on this page: Batteries - Maximizing Performance - Apple
If this continues after implementing those tips and updating your iOS, reach out to Apple Support. They would be the best equipped to investigate this behavior further.
Apple Support
Take care!