Sleep-and-charge <answer>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 <answer>USB ports</answer> are powered down, preventing phones and other devices from charging. Sleep-and-charge <answer>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 is normally powered off whenever the computer is off?
USB ports