Yeah when I used to be a mac genius, this was a common question.
From the apple store page for the adapter that is sold for EmPower ports: " Using the MagSafe Airline Adapter provides power for your computer but does not charge the battery "
As for just using the regular adapter, the other posters are indeed correct you're not gouing to get enough juice to power the unit
And with no removeable battery, your only option is to just leave it plugged in the entire time...
See
http://support.apple.com/kb/PH11206 for a quick note directly from apple