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PSA: The Galaxy S8 and S8+ doesn’t actually Fast Charge while you’re using it


The Samsung Galaxy S8 / S8+ have been available for a good few weeks now. Whether you picked one up on launch day or just a few days ago, you may noticed was how inconsistent the phone’s Fast Charging capabilities were.

The Galaxy S8 uses the same Adaptive Fast Charger as the previous year’s model, charging the device at either 9V/1.6A or 5V/2A — which is the equivalent of (and compatible with) Qualcomm Quick Charge 2.0. On a good day, the Galaxy S8 with its 3,000mAh battery go from 0% to a full charge in just 1 hour and 37 minutes. Other times you’ll find it takes much, much longer. So what gives?

Galaxy S8 can’t Fast Charge while you’re using it

Well, since Samsung is using the same Fast Charging technology in the S8 as the previous year’s Galaxy S7 and S6, the exact same caveat applies: Fast Charging only works while the screen is off. You wont find this small detail in Samsung’s spec sheet or anywhere else where they talk about the device’s fast charging capabilities — but it’s most definitely a thing. You’ll find mention of it for the S6 here, and the S7 in their own user guide.

How slow is it?

To give you a better idea of how much slower your device will charge while you’re actually using it, we were only able to reach a full a charge on our S8 after charging it for almost 3 full hours despite the device giving us the usual “Fast Charging” notification. That’s a crazy long time. Here’s what we got in our testing:

Galaxy S8 screen on charging

Projected: 1hr 37min

  • 10 min – 7%
  • 20 min – 17%
  • 30 min – 22%
  • 40 min – 34%
  • 50 min – 39%
  • 60 min – 45%
  • 70 min – 50%
  • 80 min – 55%
  • 90 min – 61%
  • 100 min – 66%
  • 110 min – 72%
  • 120 min – 77%
  • 130 min – 82%
  • 140 min – 88%
  • 150 min – 93%
  • 160 min – 97%
  • 170 min – 99%
  • 171 min – 100%

Actual: 2hrs 51 min

By comparison, the ZTE Blade V8 Pro — which features a similarly sized 3,140 mAh battery and Quick Charge 2.0 — took 1 hour 32 minutes to reach a full charge while charging with a YouTube video playing the entire time. This is how the Galaxy S8 should behave.

Looking at devices like the Google Pixel — which uses USB-PD over USB Type-C (5V/3A) to deliver “rapid charging” — charging speeds only slow when the phone’s internal temperature reaches a specific threshold, something you typically wont see unless you’re gaming. It’s still entirely possible to receive peak charging speeds while the screen is on and performing less CPU intensive tasks like messaging, or browsing Reddit. However, Samsung doesn’t give you this option on the Galaxy S8.

The OnePlus 3T on the other hand uses its own proprietary “Dash Charge” technology that is capable of fast charging while the screen is on, no matter what you’re doing. This has to do with the heat being generated by Dash Charge being handled by the 3Ts power adapter and not the phone itself.

See it for yourself

Don’t believe me? You can actually try this little test for yourself. Seeing as how the screen time out on the Galaxy S8 and S8+ caps you at 30 minutes, you’ll have to enable the “Stay awake” setting that’s tucked away inside the hidden Developer options to keep the screen on the entire time you’re charging. Here’s where you’ll find it:

  1. Go to Settings > About phone
  2. Find Build number and tap it 7 times in quick succession
  3. A notification will tell you when Developer options have been unlocked
  4. Now, go back to Settings > Developer options
  5. Turn on Stay awake (never sleep while charging)

Now, wait until your phone is completely drained — you can use this app to get you there faster — and once dead, plug it into the Samsung Adaptive Fast Charger and boot the phone back up. From there, just keep an eye on your battery percentage while your screen is on and you’ll see for yourself how much slower it’s now charging (roughly 5% every 10 minutes).

Why are you telling us this?

Since this limitation isn’t noted anywhere inside the Galaxy S8’s settings or online, we figured it’d be a good tip for Galaxy S8 and S8+ owners who may find themselves short on time and need to juice up their device as quickly as possible. Whether it’s in between flights, heading out for the night, or charging your phone on the commute home — if if you want to take full advantage of the S8’s Fast Charging speeds, plug it in, set it down, and find something else to occupy your time.

Remember, just because you see the “Fast Charging” notification while you’re using your device, doesn’t mean you’re getting the full fast charging benefits. That doesn’t happen until the screen is off.

The more you know…

Chris Chavez
I've been obsessed with consumer technology for about as long as I can remember, be it video games, photography, or mobile devices. If you can plug it in, I have to own it. Preparing for the day when Android finally becomes self-aware and I get to welcome our new robot overlords.

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