hows the battery bacup with ios 16.4 on the 12 pro

You backup data. Batteries provide the power to run your device. I think you may be asking if battery life is adversely effected by the update to iOS 16.4? And for me, it has not been an issue in any way, shape or form. It hasn't been an issue for anyone in my office either and there are many who are now updated to 16.4. Some are on iPhone X, some are on iPhone 11, 12, 13 and 14. None are having any battery issues.

Again, the battery does not "back up".

Are you asking if the battery performs any differently with iOS 16.4 compared to previous versions of iOS 16?

If that is what you are asking, the answer is that there is no difference in battery performance with iOS 16.4 than there was with previous versions of iOS 16 on the 2 iPhones here.

Other users may have different findings.

I don't understand your question? One doesn't backup a battery. One charges the battery. Please provide more details about what you are asking.