Samsung Galaxy S21 battery life — the results are in

Samsung Galaxy S21 Ultra battery tests
(Image credit: Future)

Samsung turned to big batteries and a more efficient 5-nanometer processor for powering its latest Galaxy S21 phones. Based on our testing, you'll see mixed results depending on which model you buy.

Things look good for the 6.8-inch Galaxy S21 Ultra, which lands on our best phone battery life list by lasting nearly 11.5 hours on a single charge in our battery test. Both the 6.7-inch Galaxy S21 Plus and 6.2-inch Galaxy S21 didn't fare as well, tapping out just before the 10-hour mark. That's about average for a smartphone.

We test batteries by taking a fully charged phone and setting its display to 150 nits of brightness. We then have the phone surf the web continuously over a cellular connection until it runs out of juice, timing the results. Here's a closer look at how the Galaxy S21, Galaxy S21 Plus and Galaxy S21 Ultra fared on our test

Samsung Galaxy S21 battery life results

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Row 0 - Cell 0 Battery sizeBattery test result (Hrs;Mins)
Samsung Galaxy S21 Ultra (60Hz/Adaptive)5,000 mAh11:25/10:07
Samsung Galaxy S21 Plus (60Hz/Adaptive4,800 mAh9:53/9:43
Samsung Galaxy S21 (60Hz/Adaptive4,000 mAh9:53/6:31
iPhone 12 Pro Max3,678 mAh 10:53
iPhone 122,815 mAh8:25
Samsung Galaxy Note 20 Ultra (60Hz/Adpative)4,500 mAh10:26/7:59
OnePlus 8T (60Hz/120Hz)4,500 mAh10:49/9:58
Google Pixel 5 (60Hz/90Hz)4,000 mAh10:00/9:29

The Galaxy S21 features a 4,000 mAh battery while Samsung put a 5,000 mAh power pack into the Galaxy S21 Ultra. These battery sizes are identical to what Samsung used in the Galaxy S20 and S20 Ultra. The Galaxy S21 Plus gets a bump from last year's S20 Plus, going from a 4,500 mAh power pack to a larger 4,800 mAh.

Even without a change in battery size, you'd expect to see some improvement, as the Snapdragon chipset 888 powering the new phones is supposed to be more efficient than last year's chipset. 

We certainly saw that with the Galaxy S21 Ultra, which lasted 11 hours, 25 minutes on our battery test. 

Galaxy s21 battery life

The Galaxy S21 family (Image credit: Tom's Guide)

There's one caveat about that S21 Ultra result — we got it by turning off the phone's adaptive display, which meant the display had a 60Hz refresh rate. One of the marquee features of the S21 lineup is an adaptive display that adjusts the refresh rate depending on whatever task you're doing.

Since web browsing is one of those tasks that benefits from a faster display rate, the screen is likely to stay closer to its 120Hz maximum, which would drain the battery faster. Indeed, when we turned on the adaptive display feature, the S21 Ultra's time on our battery test dropped to 10 hours and 7 minutes — a little bit better than average for a smartphone.

The Galaxy S21's time of 9 hours, 53 minutes also came with the refresh rate set to 60Hz. Turning on the adaptive display, the Galaxy S21 took an even bigger hit, dropping to 6 hours, 31 minutes on our test. That's a disappointing result any way you want to look at it.

The S21 Plus proved to be a curiosity. Even with its bigger battery, it turned in an identical time to the S21, finishing at 9 hours, 53 minutes at the 60Hz setting. Turning on the adaptive refresh rate only dropped the result by 12 minutes, the smallest difference we saw by far.

Galaxy S21 battery life versus other phones

Looking at recent flagship devices, the Galaxy S21 Ultra compares quite well, especially if you use that 11.5-hour time recorded at the 60Hz setting.

The Galaxy S21 Ultra outlasts many recent flagships, with only the iPhone 12 Pro Max getting within a half-hour of its time. The Galaxy Note 20 Ultra is particularly of interest as its 10.5-hour result was also at 60Hz. 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.

galaxy s21 battery tests

(Image credit: Tom's Guide)

All of the above phones are 5G devices, and the faster networking standard can really put a hit on battery life. That said, the S21 Ultra isn't the longest-lasting 5G phone we've tested. That honor goes to the LG V60 ThinQ 5G, which held out for nearly 13 hours. (Too bad LG is reportedly nixing a successor.) We also have a few midrange 5G phones on our longest-lasting phone list, as those devices tend to prioritize longevity over performance.

Philip Michaels

Philip Michaels is a Managing Editor at Tom's Guide. He's been covering personal technology since 1999 and was in the building when Steve Jobs showed off the iPhone for the first time. He's been evaluating smartphones since that first iPhone debuted in 2007, and he's been following phone carriers and smartphone plans since 2015. He has strong opinions about Apple, the Oakland Athletics, old movies and proper butchery techniques. Follow him at @PhilipMichaels.