Try unplugging it. Mine did the same thing, and when I disconnected it, it showed it was at 100%, even though it showed 48% when plugged in.
Also, try turning your NC completely off, wait a minute or so, then turn it back on... like rebooting a computer, it seems to fix some of these "little" things.
Is the adapter itself excessively warm? It has a breaker inside, so if it overheated or overloaded it may have tripped. If so, unplug it, let it cool off and then re-try it.