I had a similar problem, the battery would not charge at all. It worked fine until I drained the battery completely, after that the power dock would no longer charge the battery. Just as a quick experiment I connected the battery to one of my adafruit feather boards and let it charge the battery for 15 minutes, after this it worked fine again and was charged by the power dock.
Posts made by Andreas Cleverdal
RE: power dock 2 not charging