Try any or all of the following:
1. Try a different wall socket.
2. Try an Apple -approved charging cable and block, if you haven't already.
3. Go to Settings→ General→ Reset, and then select "Reset All Settings" to see if the battery stat/info resets itself to possibly display correctly.
4. Make a genius bar appointment with the nearest Apple Store to have them diagnose and possibly fix the problem for you.