A second issue experienced by users has been difficulty with charging the iPad via USB. A number of users have discovered that their iPads refuse to charge when connected to USB ports on some computers, an issue that Apple has stated is due to the required power draw for the device. In a
support document posted on the issue, Apple recommends that users charge their iPads by using either the included power outlet adapter or high-power USB 2.0 ports.The iPad's charging demand stems from its
large battery that drives a significantly hungrier device than most mobile handhelds users are accustomed to charging via USB.
Consequently, lower-power USB ports have difficulty keeping up with the iPad's draw, especially when the device is not in sleep mode.[/b]