Is the battery drain issue fixed on ios 16.5?

Protect & Prolong the life of your iPhone's Battery:

1. About the battery usage on your iPhone, iPad, and iPod touch ...
2. Batteries - Maximising Performance - Apple (IN)
3. iPhone Battery and Performance

It is a security update that protects your device from exploits. If you are looking for bug fixes, those are done in the dot releases of iOS. For a list of the updates and fixes in them, go here:

About iOS 16 Updates - Apple Support

Did 16.5.1c fix anything?