Prolong battery lifespan for iPad / iPad 2 / iPad 3: charging tips
Apple Batteries - iPad
iPhone, iPod, Using the iPad Charger
Install and use Battery Doctor HD
Battery health and maintenance App
If you're still having issues after reading through all that and trying any of the suggestions you try this:
Make sure IOS is updated to latest version
Reboot device by pressing both the home button and sleep/wake (power) buttons at the same time for 10-15 seconds until the apple logo appears on the screen, then let go.
If that doesn't work then reset the device by going to settings/general/reset/reset all settings
If that doesn't work then backup and then restore the device as new.