Hello,
Try out these troubleshooting steps for the issue you've encountered:
- Verify that the outlet being used is working.
- Try another USB power adapter if available.
- If no other USB power adapter is available, try connecting to a high-power USB 2.0 port (not a keyboard). The computer must be turned on and not in sleep or standby mode.
- Try another USB cable if available.
If you see the image below, charge the iPhone or iPod touch with USB power adapter for at least 15 minutes.

You should see this image when iPhone or iPod touch begins to charge:

If the screen still displays the low-battery icon, try turning the iPhone or iPod touch off and then on again.
If the issue persists, follow these troubleshooting steps.
from: iPhone and iPod touch: Charging the battery
http://support.apple.com/kb/HT1476
Welcome to Apple Support Communities!
Regards,
Delgadoh