If you've been having trouble with the Samsung Galaxy S8's fast-charging technology, you're not the only one but it's not a defect either.
As it turns out, the Galaxy S8 can only fast charge when its screen is off, so if you're using the smartphone don't expect it to juice up quicker than with a normal charge.
Samsung Galaxy S8 Fast Charging ... Slowly
It may not be as serious of an issue as the random reboots that have been plaguing some Galaxy S8 units, but it's still an inconvenience and it would've been nice if Samsung was upfront about it.
The company mentioned the fast-charging limitation in Galaxy S6 support pages and the Galaxy S7 user guide, but with the Galaxy S8 and Galaxy S8+ it makes no mention of it whatsoever — not in support pages, not in the user guide, not on the product page or anywhere else.
Galaxy S8 Charging Times
As Phandroid points out, it should take one hour and 37 minutes for the Galaxy S8 to juice up its 3,000 mAh battery from zero to full charge. If the phone is in use, however, it will still show the fast charging notification but it will take roughly three hours to reach full battery life.
The publication even has a detailed log listing the progression of the "fast charge" with the display on and it's a pretty painful sight.
One explanation for this fast charging limitation could be the processor. While the Snapdragon 835 powering the U.S. versions of the Galaxy S8 and Galaxy S8+ supports Qualcomm's Quick Charge 4.0, which is faster and works with the screen on as well, things are different with the in-house Exynos 8895 processor powering the global versions of the smartphones.
With this in mind, Samsung might have chosen to add the fast charging limitations to both models so as not to add further differences.
Just Let It Charge
In conclusion, if you're in a hurry and you need your Samsung Galaxy S8 or Galaxy S8+ charged as soon as possible, let it charge without using it. It will take significantly less with the display off, since fast charging will kick in.
That said, the Galaxy S8 and Galaxy S8+ are still among the most powerful smartphones currently available on the market, packing a slew of top-notch specs and features to make them worthy of the flagship title.
Samsung is also expected to release a high-end Galaxy Note 8 later this year, packing even more impressive specs than the Galaxy S8 series. Rumor has it that the Galaxy Note 8 will feature the in-display fingerprint authentication and dual rear camera setup that were previously rumored for the Galaxy S8, but never made it. There's a good chance, however, that the Galaxy Note 8 will come with the same fast charging limitation as the Galaxy S8 line.