According to a recent battery test run by Tom’s Guide, to no one’s surprise, using 5G on the iPhone 12 proved to be a massive battery drain. Based on their tests, using 5G on the iPhone 12 and iPhone 12 Pro resulted in 2 hours less battery life compared to using 4G. On the iPhone 12, the phone lasted for about 8 hours 25 minutes on 5G, and 10 hours and 23 minutes on 4G.
The iPhone 12 Pro fared a bit better, with 9 hours 6 minutes on 5G, and 11 hours 24 minutes on 4G. To give you some context, the iPhone 11 and 11 Pro, both of which only support 4G, lasted about 11 hours 16 minutes and 10 hours and 24 minutes respectively, the latter of which is rather strange.
As for the Android competition, battery life seems to be better on 5G either and they found that the Samsung Galaxy S20, S20 Plus, and the OnePlus 8T lasted about 9 hours 31 minutes, 10 hours 31 minutes, and 10 hours 49 minutes respectively.