Here's why your Galaxy S8 might not actually be fast-charging
Need to charge your Galaxy S8 in a hurry? Don't use it while it's charging.
The Galaxy S8 and S8 Plus come with rapid charging features and an Adaptive Fast Charger in the box, which charges your battery at super-fast speeds. Even with the feature enabled, though, your Galaxy S8 might not always use Fast Charging. Here's why and what you can do about it.
How to enable Fast cable charging on the Galaxy S8
Fast charging can be turned on and off in the settings. To make sure it's on, go to Settings > Device maintenance > Battery > Advanced settings and toggle on Fast cable charging.
With this enabled, when you plug your Galaxy S8 or Galaxy S8 Plus into the provided Adaptive Fast Charger or a Qualcomm Quick Charge 2.0 charger, it should take you from 0 to 100 percent in approximately 2 hours.
Fast charging doesn't always work
Even with this enabled, your phone won't always fast-charge, as Chris Chavez of Phandroid points out. If you are using the phone or the screen is left on while the phone is charging, the phone will charge much slower. In his testing, Chavez found that it took nearly 3 hours to fully recharge the Galaxy S8 with the screen left on -- about the same duration as "regular" charging. He says:
"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."
You won't find that helpful little tidbit anywhere in the Galaxy S8 documentation.
This isn't the first time there's been a catch to rapid charging. Chavez notes that the Google Pixel will disable rapid charging when the internal temperature of the phone surpasses a certain threshold.
In my time with the Galaxy S8 Plus, I've noticed a significant difference in how quickly it charges when I'm trying to top off the battery and constantly using it. But it hadn't dawned on me that fast charging isn't actually working when the screen is on or the phone is in use.
That being the case, if you need to quickly charge your Galaxy S8 before leaving the office or heading out for the night, it's best to plug it in and walk away for a while.
Check out out other Galaxy S8 tips: