Looking around, but not finding a definitive answer. Is this unit capable of charging with the USB cable, or do I need to use the supplied charger at all times?
If when you plug the USB in ..there appears a large green battery on the screen for a moment ..it will charge via the USB.
Even if you do not get the battery ...a small thunderbolt should show up in the taskbar. That means it does charge via USB.
At least that is the way it is on my Vi30W, and I would not think they would do differently on the 40, given both us use 4.0, same chipset. I get the large battery symbol whether the tab is on, in standby or off completely.