star trek - How is Data powered?

What powers Data from Star Trek The Next Generation? Did he generate his own internal power or did he have to plug into the Enterprise periodically to recharge? Or perhaps a combination of the two?

Answer

From the transcript of Insurrection:

                                      ARTIM
                         Don't you ever get tired?

                                       DATA

                         My power cells continually re-
                         charge themselves.

So he is powered by "power cells" that continually recharge themselves, therefore apparently he does not have to plug into the Enterprise to recharge.

Indeed there is also the episode where his head is stuck in the cave (Time's Arrow) for over 500 years, and it still works fine afterword.