Why is my brand new S21 battery draining so fast?

That’s perfectly fine, as long as your 5G coverage is decent, but keeping 5G enabled all the time could have a negative impact on battery life . To be precise, 5G will disable automatically when you’re not in a 5G area, so there’s not much to worry about in this one scenario.

Turning the Note 20 Ultra’s adaptive display feature on reduced the time by 2.5 hours, so obviously the S21 Ultra does a better job at conserving power even with a high refresh rate hitting its battery. All of the above phones are 5G devices, and the faster networking standard can really put a hit on battery life. 10 Mar 2021

According to SamMobile, when the phone or rather the OIS detects shaking or motion, the camera app will wake the device. And because, as Wander pointed out, Samsung isn’t releasing the wakelock that holds the camera sensor in place when the device is moving around , it causes battery drain in the background.

The Galaxy S21 series supports up to 120Hz display which makes your display smooth but it can also quickly drain the battery faster because of its high screen refresh rate . The standard refresh rate is more than enough for most users and won’t have any noticeable difference in the experience between the two.