You probably read the article about the iPhone 12 series losing too much battery life during hibernation.
But that is not the whole story about the battery problems with iOS 14.2, because now it turns out that older iPhones also have problems, and even bigger.
Note that we upgraded the rating of the iPhone 12 Pro Max after first testing the phone with an iCloud backup, which we thought led to poorer battery life.
After lengthy testing with a full-formatted device, we found that battery life was better and upgraded to 9 out of 10. Whether these issues are related is uncertain, but we do not think so, and it does not seem that we are close to a solution.
We have experienced this
We believe that there is something in iOS 14.2 that creates problems, for back to the older models (iPhone 7, 6s, Xs, etc), then there are reports of losses of over 50 percent in less than 30 minutes and five percent at normal use. It is so much that the mobiles become useless.
Apparently, the iPad Pro from 2018 will also be affected by these iOS 14.2 errors.
Again: we gave the iPhone 12 Pro 8 out of 10 due to low battery and it is still current and not a problem fixed with iOS 14.3 beta 3 that was just installed. We experienced after iOS 14.3 beta that the battery was drained even faster.