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Galaxy S9 battery life isn't as good as we had hoped

After more than four months of testing, our results are in.

James Martin/CNET

I had high hopes for the Galaxy S9's and Galaxy S9 Plus' battery life when Samsung announced the two phones in late February.

Despite the fact that the Galaxy S9 and S9 Plus have the same battery capacities as last year's Galaxy S8 and S8 Plus -- that's 3,000mAh and 3,500mAh respectively -- I expected them to exceed 2017's phones in battery life. Or at least unquestionably meet the same standard.

The main reason for that expectation is the Qualcomm Snapdragon 845 processor that lives inside the Galaxy S9 and S9 Plus phones in the US and other countries. Samsung equips the Galaxy phones in some regions with its house-made Exynos chip, but it's the Snapdragon 845 we tested most.

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The Galaxy S9 and S9 Plus have the same battery size as last year's models.

Josh Miller/CNET

Qualcomm promised that its Snapdragon 845 chipset would deliver 30 percent greater power efficiency than 2017's Snapdragon 835 chipset, which drove the Galaxy S8 and S8 Plus. Those stated battery savings imply that the Galaxy S9 and larger S9 Plus would run longer on a single charge than those two S8 phones, which use the Snapdragon 835 chip.

Instead, the Galaxy S9's battery cut out sooner than the Galaxy S8 phones in our looping video battery drain test. The Galaxy S9 Plus fared better, outlasting the Galaxy S8 Plus in our battery tests, but only by a 4 percent margin. And even that gain is far smaller than the optimal battery savings suggested by the Snapdragon 845 chip. (See details below.)

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Balancing long battery life with powerful features is a tricky business.

Josh Miller/CNET

Granted, our video lab test is a very specific indicator of performance; it doesn't paint the full picture of phone use, like loading up websites and downloading images, streaming videos and navigating in Google Maps. And it doesn't guard against phonemakers that "optimize" their software for precisely this kind of assessment. But our test does provide a baseline that's useful for comparison, one that goes beyond casual observation.

On the other hand, pure observation showed that both Galaxy S9 and S9 Plus phones drained much slower than the Galaxy S8 and Galaxy S8 Plus when I wasn't actively using them (that's good). Again, I break all of this down below, so stick with me.

I've kept an eye on battery drain since I began using the Galaxy S9 Plus almost exclusively this March. And while the phone will last me from morning to night on a single charge, I'm disappointed that either the Galaxy S9 Plus isn't taking advantage of the Snapdragon 845's promised battery boost, or the chip is perhaps only theoretically more efficient.

The party to "blame" is hard to parse out since software and hardware work together to manage the phone's battery resources.

Now, read on for lab test results, idle drain comparisons and what you can do to manage a Galaxy S9 phone's battery life.

Galaxy S9 and S9 Plus lab test results

We put three different Galaxy S9 units (one with the Exynos processor) and four Galaxy S9 Plus phones through our video drain test. Some of these phones were loaned to us by Samsung, some we purchased. The results were all over the map, which frustrated us incredibly, so we ran the tests over and over again.

The numbers below represent the average of the Galaxy battery drain test results  -- minus the Exynos unit -- compared with our average results from multiple Galaxy S8 and S8 Plus devices. Note that the Galaxy S8 and S9 phones have the same screen size: 5.8 inches for the smaller devices and 6.2 inches for the Plus versions. The comparable screen size means that no phone automatically draws more power to light up a larger screen than the generation before. 

The chart also shows how many hours of battery life we'd expect to get compared with the Galaxy S8 scores, assuming that we saw a 30 percent boost in power efficiency from the Snapdragon 845 processor (that's a theoretical number; real-world results are often lower).

Galaxy S9 battery test results (Snapdragon 845 chipset)


Battery capacity CNET video drain test average* Best-case battery life from 2017 Galaxy S8/Plus (+30%) Tested percentage change from 2017 Galaxy S8/Plus
Galaxy S9 3,000mAh 15 hours, 30 minutes (15.5 hours) 20 hours, 9 minutes (20.15 hours) -3.1%
Galaxy S8 3,000mAh 16 hours N/A N/A
Galaxy S9 Plus 3,500mAh 18 hours 23 hours, 24 minutes (23.4 hours) 4%
Galaxy S8 Plus 3,500mAh 17 hours, 18 minutes (17.3 hours) N/A N/A

*Looping video in airplane mode, screen brightness and headphone volume set to 50 percent (default resolution)

Finally, you see the battery gains and losses from our tests compared with last year's Galaxy S8 results. The Galaxy S9 died sooner than last year's Galaxy S8 (a change of -3.1 percent) and the Galaxy S9 Plus yielded 4 percent better battery life over the Galaxy S8 Plus; an improvement, but not the knockout we had hoped for.

samsung-galaxy-s9-plus-unboxing-21
Andrew Hoyle/CNET

We also ran battery tests on a Galaxy S9 using Samsung's Exynos 9810 chipset, for an average of 15 hours, 20 minutes' run time on a single charge.

What this result means: That the Galaxy S9 and S9 Plus should give you about the same battery life as last year's Galaxy S8 and S8 Plus when you're actively using them. 

Galaxy S9 battery has better idle drain than the Galaxy S8

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The Galaxy S9, left, and S8 share the same screen size and battery capacity.

Josh Miller/CNET

If your battery isn't actively charging, it's discharging. All phones will lose battery capacity even when you're not "using" them. That's referred to as idle drain -- the phones are still running apps and processes, checking messages, pinging for data and so forth.

To test out if the Galaxy S9 drained faster or slower than the Galaxy S8, I fully charged both phones, turned brightness to 50 percent, turned on airplane mode and pulled them off the plug at the same time. Then I kept track of their percentages over the course of the next week.

The Galaxy S9 drained significantly slower than the Galaxy S8 over time. After 72 hours, the Galaxy S9 had lost 50 percent of its battery life, whereas the Galaxy S8 had lost 59 percent.

Seven days after starting the test, the Galaxy S8 battery reserves gasped their last, while this year's S9 still has 25 percent to go.

What this result means: The one variable I couldn't account for is how fresh the S8's battery is. Batteries lose capacity as they age, and the Galaxy S8 had more hours of use over the course of its lifetime than the Galaxy S9 when I started this test, though this particular unit was only lightly used over the last year.

Samsung Galaxy S9 and S9 Plus
Sarah Tew/CNET

While the idle drain test isn't scientifically bulletproof, the wide percentage gap suggests that the Galaxy S9 has a longer standby time than the Galaxy S8.

Real-world battery use

The Galaxy S9 Plus loaner phone that I've been using nearly every day reliably lasts me from 6 a.m. through 10:30 p.m., though there are nights when the battery reserves hover under 10 percent by the time I go to bed. Other days of lighter use, I might hit the hay with 20 or 30 percent left.

When I'm home, I'm happy to let battery levels approach the brink. A charge is just a few feet away. But when I'm out, a steady slide into the single digits is too risky. I feel compelled to top up the S9 Plus when I know I'm going out.

As on any phone, maps navigation, uploads, downloads, and video and audio streams can rapidly suck up battery reserves. But even after my morning routine of checking in on social media and reading the news, I'd notice that the battery often dropped to 80 percent within 2 hours, and often to the 70 percent range 3 hours after waking up.

The Galaxy S9 Plus has never died on me before 10:30 p.m., but it's gotten close.

What this result means: Don't count on the Galaxy S9 to take you from morning to the wee hours. As with most phones, if you're looking at a late night, take a charger or battery pack with you or prepare to turn on power-saving mode after hours.

How to make the Galaxy S9 battery last longer (without installing other apps)

No phone is immune to battery drain, and the more heavily you use it (especially streaming media and maps navigation), the faster those power reserves run dry. The Galaxy S9 and S9 Plus have some built-in battery settings to help keep the phone alive longer.

  • Turn off Wi-Fi and Bluetooth when you aren't using them.
  • Turn on Wi-Fi power-saving mode, which will reduce battery usage when you're not actively on Wi-Fi.
  • Turn on two levels of power-saving mode. This will decrease brightness, limit your CPU speed (the phone will work a little slower), disable the Always-On display and may drop the screen resolution.
  • Select apps that don't draw power when you aren't actively using them.
  • Select apps that will never run in the background.
Now playing: Watch this: Galaxy S9 mostly aces our real-world tests
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Hope for longer battery life is on the horizon

Samsung knows battery life is a flashpoint for buyers, and is already promising long life for its upcoming Galaxy Note 9. The phonemaker teased all-day battery life in a video posted ahead of its August 9 Unpacked event. Clearly, extending battery life is on Samsung's mind, and we can hope the company is able to make gains with 2018's Note 9 and 2019's Galaxy S10.

This story first published July 28 at 4:00am PT and most recently updated July 30 at 2:20pm PT.

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