If the iPad is plugged in and the battery icon says Not Charging rather than showing the lightning bolt it probably means it is plugged into a UDB port that isn't providing sufficient voltage (computer, powered USB hub) to charge the iPad while it is operating. If you turn the iPad off or if it goes to sleep while plugged into one of these USB ports it will charge but at a slower rate than if the original 10W wall wart was used. They will also supply sufficient current, I believe, to keep the battery from discharging while the iPad is in use. If you want to both charge and use your iPad you need to plug it into the 10W charger that came with it.