I just bought myself and my boyfriend the Kangertech Cupti for Christmas. Mine works perfectly fine, but my biyfriend's won't charge externally or directly on device. I swapped out the batteries and tried using mine on his and he still gets the same display that the battery is very low(I fully charged my battery then put it in his device). When directly charging it through the device the screen will continuously give me the display that the battery hasn't charged at all (the battery icon with the blocks inside the icon telling you how much the battery is charged).
I even left it on the charger for a good 3 hours and no change.
The dealer I got it from couldn't do anything about it they claimed.