Although Google presented the Google Nexus 7 with much aplomb, some issues have been reported in the smartphone recently. A notable number of users have complained about Nexus 7 slow charging issues. Users have complained that their Google Nexus 7 takes 10 long hours for it to get fully charged! This is quite a drag compared to the two hours that most smartphones take to be charged.
While some relate this issue to the latest KitKat 4.4.2 update on their smartphones, the real cause can be pinned to the USB slot or connector.
If your Nexus is still covered under warranty, then all you could do is get in touch with customer care. However, for the less lucky owners, try and detect the main cause for the issue. Experiment with charging on the dock, via laptop or on the plug board. Check if either helps you fix the issue.
Perhaps re-plugging or pulling out the connector from the wall plug broad multiple times could help.