So you have you or have you not tried different cables and different chargers?
I just tested all of my USB cables and 25% of them were dud, one of them (an Anker one) would cause drain rather than charge.
It is probably the cable, they fail most often, followed by the Powercore followed by the Powerport.
All I'm suggesting this for is because you can nail the warranty in 1 email rather then Anker ask you to to test as per my suggestions. Anker need the serial number (off the packaging) and then they usually just ship a replacement to you and so you're whole in a few days.