Samsung has turned to a bigger battery and a more efficient 5-nanometer processor to power its latest Galaxy S21 phone. Based on our tests, the results are mixed, depending on which model you buy.

The 6.8-inch Galaxy S21 Ultra lasted nearly 11.5 hours on a single charge in our battery tests, ranking it on our best smartphone battery life list. The Galaxy S21 with the smaller 6.2-inch display fared less well, running out of battery just before the 10-hour mark. This is an average level for a smartphone.

Battery testing is done by taking a fully charged phone and setting the display brightness to 150 nits. We then let the phone surf the web continuously until the battery runs out and measure the results. The test results for the Galaxy S21 and Galaxy S21 Ultra are as follows. (Results for the Galaxy S21 Plus will be added as soon as we get a chance to test this phone.)

The Galaxy S21 has a 4,000 mAh battery, while Samsung has a 5,000 mAh power pack in the Galaxy S21 Ultra. These battery sizes are the same as those used by Samsung in the Galaxy S20 and S20 Ultra, but the Snapdragon chipset 888 in the new models is more efficient than last year's models.

Our battery tests certainly confirmed that with the Galaxy S21 Ultra, which lasted 11 hours and 25 minutes.

There is one caveat to the S21 Ultra results. These results were obtained with the phone's adaptive display turned off, and the display's refresh rate was 60 Hz; one of the key features of the S21 lineup is the adaptive display, which adjusts the refresh rate based on whatever task is being performed.

Web browsing is one of the tasks that would benefit from a faster display rate, so the screen is likely to be closer to the maximum 120 Hz, which would drain the battery faster. In fact, with the adaptive display feature turned on, the S21 Ultra's battery test time dropped to 10 hours and 7 minutes.

The 9 hours 53 minutes on the Galaxy S21 was also based on a refresh rate set at 60 Hz. With adaptive display turned on, the Galaxy S21 took an even bigger hit, dropping to 6 hours and 31 minutes in the test. This is a disappointing result by any measure.

Looking at recent flagship devices, the Galaxy S21 Ultra compares much better, especially with 11.5 hours recorded at the 60 Hz setting.

The Galaxy S21 Ultra lasts longer than these recent flagship devices, with only the iPhone 12 Pro Max recording a time under 30 minutes. the Galaxy Note 20 Ultra's result of 10.5 hours at 60Hz is also particularly interesting Turning on the Note 20 Ultra's adaptive display feature reduced the time by 2.5 hours, so clearly the S21 Ultra is better at conserving power, even when the battery is overloaded at higher refresh rates.

All of the above phones are 5G devices, and faster network standards can take a big hit on battery life. That said, the S21 Ultra is not the longest-lasting 5G phone we tested. That honor goes to the LG V60 ThinQ 5G, which held up for nearly 13 hours. Several mid-range 5G phones also made the list of longest-lasting phones. This is because these devices tend to prioritize longevity over performance.