[Samsung Galaxy S21 Ultra] PirateYarr:
Here is a test I did on my S21 Ultra (Exynos), that started a bit spontaneously with me wondering about the impact on battery of different refresh rates and resolutions, together with use cases (touching the screen or just looking at it). So I started playing around and landed in some kind of improvised test.

The phone is an S21 Ultra Exynos model, as already mentioned. The model number is SM-G998B/DS. The FW was G998BXXU2AUBB.

The test was performed at 20% screen brightness and 30% battery left on the phone. The phone was charged between tests to hover around 30% battery, +/- 2%, i.e. it was between 28% and 32% during the tests.

There were two types of tests; "Screen Interaction Test" that intended to find the current consumption while repeatedly touching the screen and therefore keeping the CPU ready, and an "Idle Current Consumption Test" where the screen was just turned on for 3 minutes without interacting with the phone. In both tests, the phone was running the app Ampere in the foreground, thus displaying it.

The data logging was done manually by me watching the app Ampere and noting down its shown current consumption every second into a Google Sheets document. Ampere collects 50 data points, discards the 10 lowest and 10 highest, then takes the average of the remaining 30 points before presenting the current consumption. These values were gathered for 5 minutes in the interaction test, and 3 minutes in the idle test, in order to acquire a robust sample set that was resilient against temporary peaks in current consumption. Since I don't have control over the phone's background processes, it was possible that a background task would cause a sudden peak in current consumption. Averaging these values makes the measurement more resilient against such peaks.

The phone was put in Airplane Mode in order to eliminate Wifi, 4G, Bluetooth and all those things from the measurement.

Test Results​

Interacting With Screen in 120 Hz Adaptive Refresh Rate and Different Resolutions​

The screen was tapped 3-4 times per second in order to keep it active. The phone was displaying the app Ampere. Test duration was 5 minutes and data was logged about every second from Ampere, and then averaged over the entire test duration.

HD 120 Hz Adaptive Refresh Rate: 204 mA

FHD 120 Hz Adaptive Refresh Rate: 184 mA

WQHD 120 Hz Adaptive Refresh Rate: 206 mA

View attachment 5255207

Interacting With Screen in 60 Hz Adaptive Refresh Rate and Different Resolutions​

The screen was tapped 3-4 times per second in order to keep it active. The phone was displaying the app Ampere. Test duration was 5 minutes and data was logged about every second from Ampere, and then averaged over the entire test duration.

HD 60 Hz Standard Refresh Rate: 175 mA

FHD 60 Hz Standard Refresh Rate: 161 mA

WQHD 60 Hz Standard Refresh Rate: 176 mA

View attachment 5255211

Idling With Screen On in 60 Hz Standard Refresh Rate and Different Resolutions​

The screen was turned on it displayed the app Ampere. The screen was not interacted with at all for the whole 3 minutes this test took. The test was only done for 60 Hz because there is no point in doing it for 120 Hz since the screen drops down to 60 Hz when idling in the app Ampere. The values are the average value of the entire test duration (3 minutes).

HD 60 Hz Standard Refresh Rate, Screen Idling: 144 mA

FHD 60 Hz Standard Refresh Rate, Screen Idling: 145 mA

WQHD 60 Hz Standard Refresh Rate, Screen Idling: 147 mA

View attachment 5255213

Bonus Test: 48 Hz and 96 Hz Display Mode​

The two hidden display modes were also tested but there were no advantages in using these modes regarding current draw. Plus, these modes actually tint the display slightly greenish in my opinion and in my phone. YMMV.

TLDR/Conclusion​

The most efficient resolution is FHD when the phone is actively used. However, while not interacting with the screen, the resolution has almost no impact on battery consumption. Note: the resolution probably affects a lot when gaming is involved, which I have not tested. Between 120 Hz Adaptive and 60 Hz Standard, the current draw is about 15% to 17% higher for 120 Hz Adaptive Mode, depending on resolution. In other words, running the phone at 120 Hz does not exactly eat up the battery, which is very good to see!

A quick word about the current draw numbers: the current draw will be lower when the battery is charged more, since the battery voltage will be higher in that case. The lower the voltage, the greater current draw to keep power constant. At full charge, these numbers would be 88% of the ones I had at 30% battery charge. This should not change the relative numbers, i.e. FHD 120 Hz Adaptive Mode should still draw about 15% more current than FHD 60 Hz Standard Mode, I think.