I lost track of how you were charging the iPad, so I offer the following as a general FYI.
The iPad requires a 10W power source, such as the wall charger that came with it, to charge at normal speed. If you continue to use the iPad while charging, it will take longer.
Newer Macs, PCs and powered hubs usually come with high-power USB 2 ports, but that means 5W of power. Very old Macs and older and inexpensive PCs provided only 3W (some hubs or some hub ports, in fact, may not provide any power).
When you charge the iPad thru ports that do not provide 10W of power, the message "Not Charging" appears in the status bar next to the battery icon, when you look at it. In fact, the iPad will charge, but only when it's in sleep mode.
Also make sure your computer is on while charging the iPad via USB. If the iPad is connected to a computer that’s turned off or is in sleep or standby mode, the iPad battery will continue to drain.
Hope this explained some of your concernes,
Rysz