Morpheus: The human body generates more bio-electricity than a 120-volt battery and over 25,000 BTU's of body heat. Combined with a form of fusion, the machines had found all the energy they would ever need.
Morpheus: And standing there, facing the pure horrifying precision, I came to realize the obviousness of the truth. What is the Matrix? Control. The Matrix is a computer generated dream world, built to keep us under control in order to change a human being into this.
[holds up a copper-top D cell battery]
Neo: No. I don't believe it. It's not possible.
Morpheus: I didn't say it would be easy, Neo. I just said it would be the truth.