Please try the following:
iPod® and iPhone® troubleshooting
My device will not charge when docked. What should I do?
- If your device is in a case or protective sleeve, remove it and then reseat it on the connector. If it is not seated correctly on the connector, it may prevent charging
- Try resetting your device. Depending on your model, you should refer to Apple® support to perform this task
- Reset your SoundDock® system. Turn the system off and unplug it from the power for 60 seconds. Once you have reconnected the system to the power, see if the device will charge