Thank you for being with Samsung and sharing your concern. We would like to inform you that in order to increase the charging speed, turn the device or its screen off when you charge the battery. While charging the battery when the device is turned off, the icon appears on the screen. If the fast charging feature is not activated, launch the Settings app, tap Device maintenance → Battery → → Advanced settings, and then tap the Fast cable charging switch to activate it. We would also like to inform you that You cannot use the built-in fast charging feature when you charge the battery using a standard battery charger. Be sure to hit ♡ when you find an answer that works for you.