The plot of The Matrix was supposedly originally based on the humans’ brains used as the hardware substrate for running the computers’ programs – if you like, human brains as CPUs – explaining why the computers needed to keep humans alive in tanks but in a dream-like state.

This was deemed to confusing for audiences to understand, so the story was changed so that humans became the power source for the machines. Since humans take in a lot more energy (food) than they produce as heat (or “bioelectric power”), this makes zero sense. In a future world driven by physics as we understand it, the machines would be better off killing all the humans and using some other power source.

The brains-as-CPUs version of the story is both physically plausible and a lot more interesting than the humans-as-batteries version. So some Matrix fans maintain that this is what was happening in the movie, with the human battery explanation just Morpheus’s misunderstanding.