A battery life test by Arun Maini of the YouTube channel Mrwhosetheboss found that the iPhone 11 Pro and 11 Pro Max had significant leads in battery runtimes compared to the newer iPhone 12 and 12 Pro. The iPhone 12 and 12 Pro have a 2,815 mAh battery, which is not only lower in terms of actual capacity than the previous generation but also powers larger and higher resolution displays leading to lower runtimes.
https://www.notebookcheck.net/iPhone-12-and-iPhone-12-Pro-s-battery-runtimes-fail-to-impress-when-compared-to-the-iPhone-11-Pro.499155.0.html