<answer>Sleep-and-charge USB ports</answer> can be used to charge electronic devices even when the computer is switched off. Normally, when a computer is powered off the USB ports are powered down, preventing phones and other devices from charging. <answer>Sleep-and-charge USB ports</answer> remain powered even when the computer is off. On laptops, charging devices from the USB port when it is not being powered from AC drains the laptop battery faster; most laptops have a facility to stop charging if their own battery charge level gets too low.
What remain powered even whenever the computer is powered off?
Sleep-and-charge USB ports