Adam Doud/ZDNET

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ZDNET's key takeaways

• Total battery capacity is only one factor influencing actual device longevity.
• Lab tests demonstrate how different hardware components impact power consumption rates.
• Efficient processors and screen settings are crucial for maximizing battery performance.

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Battery size is not always a straightforward comparison. The highest number of milliampere hours (mAh) doesn't always translate to the longest battery life. Indeed, "battery life" itself is somewhat subjective. A phone streaming a video saved to local memory will last longer than a phone exporting a 30-minute 4K video, and yet another phone streaming Spotify to a car on a road trip (with the screen off) will last longer than both.

As you might have gleaned from that, the main things that will chew up your battery the fastest are the screen and the processor. The waters get muddied a bit further when you consider things like an AMOLED panel versus an LED screen. Suffice it to say, there are a lot of factors to negotiate.

Also: I changed 7 settings on my Samsung phone for significantly improved battery life

So when OnePlus launched the OnePlus 15R with a 7,400mAh battery and noted that it's the largest battery in a phone you can buy in the US, we took notice. Then we said, "Prove it." We decided to put that battery size to the test in two different ways. First, we conducted a local 4K video streaming test, and then we performed a battery rundown test using PC Mark. Both sets of results were surprising in different ways. Here's what happened.

How we tested

To start, we chose the phones we wanted to test. In the US, there are only a few manufacturers to choose from -- Samsung, Google, Motorola, Apple, and OnePlus. I don't have the largest offerings from Apple or Motorola (and testing a flip phone against the OnePlus 15R wouldn't yield much useful information), so I limited my test phones to the OnePlus 15, OnePlus 15R, Samsung Galaxy S25 Ultra, and the Google Pixel 10 Pro XL. 

The first test I ran was PCMark's Work 3.0 Battery Rundown test. This test runs the benchmark in a cycle, testing web browsing, video editing, writing, photo editing, and data manipulation in a loop until the phone's battery reaches 20%. Then, it tells you how long it took the phone to get there.

Adam Doud/ZDNET

For the video playback test, I stole this idea from YouTuber and fellow ZDNET colleague Christian De Looper (who performs a ton of head-to-head battery tests on his channel). I use a 4K version of the movie "The Avengers" and play it on a loop with VLC. 

Also: I changed 7 settings on my Samsung phone for significantly improved battery life

The phones are all put into Airplane mode with Wi-Fi and Bluetooth both disabled. Screen brightness gets set to 100% and the volume set to 25% -- because you can only listen to the Hulk's roar so many times before you want to pull your hair out. Then I set up a camera to video them and capture the exact time they shut down.

Here are the results.

Video playback test:

Battery size (mAh)

Video playback time

PCMark

Google Pixel 10 Pro XL

5,200

19:37:56

12:34

Samsung Galaxy S25 Ultra

5.000

25:56:26

11:32

OnePlus 15

7,300

30:58:28

13:18

OnePlus 15R

7,400

28:36:00

11:10

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Video playback test

For the video playback test, I pressed play simultaneously and let them run. The first phone to take its ball and go home was the Pixel 10 Pro XL, which featured a 5,200mAh battery. The Pixel 10 Pro XL lasted less than one day, at 19:37:56. The next to fall was the Samsung Galaxy S25 Ultra's 5,000mAh battery, after 25:56:26. Then, interestingly enough, the OnePlus 15R checked out at 28:36:00, while the OnePlus 15 lasted 30:58:28; its 7,300mAh battery outlasted the 15R's 7,400mAh cell.

Also: How to clear your Android phone cache (and wipe out lag for good)

Both the OnePlus 15R and the OnePlus 15 have similar screens -- they're both AMOLED with 1800 nits of brightness in high-brightness mode. The OnePlus 15R has a slight larger screen at 6.83 inches versus the 6.78 inches of the 15. The OnePlus 15 also has a (theoretically) higher efficiency processor in the Snapdragon 8 Elite Gen 5 versus the Snapdragon 8 Elite. That combination of factors is probably what accounts for the OnePlus 15 outlasting its younger sibling.

PCMark test

Where things got really interesting was the PC Mark battery test. During that test, the OnePlus 15R fell first at 11:10, followed by the S25 Ultra at 11:32. Then the Pixel 10 Pro XL lasted 12:34, and the OnePlus 15 clocked in at 13:18. The key difference here was likely in the processors, since this test is all about processing -- video editing, data management, etc. 

The Tensor 5 chip in the Pixel 10 Pro XL, according to Google, was designed with power efficiency in mind over raw power, which is a good approach in this case. The Snapdragon 8 Elite Gen 5 also exhibits similar power efficiency compared to the previous generation, the Snapdragon 8 Elite, which is found in the Samsung Galaxy S25 Ultra. Still, I expected the OnePlus 15R to perform better here.

Bottom line

All this goes to show that battery life really is a mix of a lot of different factors. Just like more megapixels don't necessarily mean better photos, and more cores don't necessarily equal more power, bigger batteries don't necessarily translate to enhanced stamina. It's a significant piece of the puzzle, but it's not the whole picture.