@Deiru actually for once I wouldn't be sure that they didn't - The Matrix caused a short lived fad where mainstream people went philosophical and kept discussing the "ideas in the movie" to the point where there were books that people actually wrote and bought on the subject.
So yeah I think if the studio did choose to leave that in people would have noticed.
As many times as I have heard or participated in this discussion about matrix I have never heard a single person actually acknowledge the fact that humans were batteries.
Just being "loaded into matrix" seemed enough, and nobody really cared why they were loaded.
At least that's how it was for my peers at the time. (And still)
But Russia was a crazy place. Some here still think that Matrix invented cyberpunk.
@polychrome I take it back, I have just read exactly the analysis that used the batteries metaphor, so I guess you are right.