Hey there tom-asse,
Thanks for reaching out to Apple Support Communities. Congratulations on getting your iPhone 11 Pro. I understand you have some concerns about using the Optimized Battery Charging feature on your iPhone. I’ll be happy to help.
Optimized Battery Charging is active only when your iPhone predicts that it will be connected to a charger for a long period of time. With a new iPhone, it may not be charging long enough for it make this prediction. You can read more about this here:
About Optimized Battery Charging on your iPhone
Also, if you haven’t already, update your iPhone to iOS 13.1.2. In the 13.1 update, there is a mention of the Optimized Battery Charging feature. Read more about this here:
About iOS 13 Updates
You can read how to back up your iPhone and update here:
How to back up your iPhone, iPad, and iPod touch
Update your iPhone, iPad, or iPod touch
Cheers