You may have asked yourself the question “Why isn’t my iPad charging when connected to the computer?” Here’s why: Unlike most devices that plug into your computer’s USB port, your iPad may tell you it’s not charging when connected in this manner. Why? Because your USB port isn’t supplying enough power.
If you don’t have your AC adapter handy, try plugging the iPad into a different USB port. The wattage delivered to each port varies. For example, USB ports in the rear of desktops usually are higher power than those in the front.
And if changing ports doesn’t work? Turn off the screen on your iPad and leave it plugged in. It will charge, very slowly.
Or, just use your AC Adapter and plug it in the wall outlet. This is the fastest way to charge the iPad.