From the 1996 draft:

Morpheus: Without the sun, the machines sought out a new energy source to survive. They discovered a new form of fusion. All that was required to initiate the reaction was a small electric charge. ... The human body generates more bio-electricity than a 120-volt battery and over 25,000 B.T.U.'s of body heat ... We are, as an energy source, easily renewable and completely recyclable ... All they needed to control this new battery was something to occupy our mind.

This still makes more scientific sense than the final version, which said that humans were the actual source of energy rather than the batteries for the energy source.

After more googling:

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"The only "official statement" I know of is an off-hand comment from one of the brothers on the DVD commentary for one of the director's cuts (I forget which but I think its on the Ultimate Matrix Collection.) He is discussing the whole setup for the Matrix and mentions that they "originally had a different idea" before dismissing the question as irrelevant to the story. (e.g. it doesn't matter to him why the machines did what they did, as its just a plot device to get the story started.)

More details about what that original plan was come from some written material based on early pre-release information from the movie. Specifically, Neil Gaiman's short story "Goliath" is set in the Matrix universe and includes this alternate view. I have also heard that the "novelization" of the Matrix included this idea but there's no such novel that I know of; its possible that a novelized version of an early script exists (there's a published version of the shooting script for sale but that includes the story as filmed.)"
https://scifi.stackexchange.com/questions/19817/was-executive-meddling-the-cause-of-humans-as-batteries-in-the-matrix

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... time to revisit the Ultimate Matrix Collection.
I watched all five DVDs in one weekend (don't even know how many hours of material is on them ) and it's all blurry :)

I did return to the film critics/philosophers' commentary of the movies and took notes; should revisit the other material too...

and yes, "Goliath" hints at that idea... but that's no 'direct' proof this was the original version of the Wachovskis... Gaiman is known to put his own spin on mythology in everything he writes.

https://www.joe.ie/tech/nokia-are-bringing-back-the-very-cool-phone-from-the-matrix-with-a-20-day-battery-life-and-cheap-price-617495

Aristot. Poet. 1450b



looks like something the Wachowskis have read before writing those scripts...

"Reeves has proven over the roughly 30 years of his acting career to be an essentially generous and curious performer with a near-beatific ability to be utterly present. This is often mistaken for a blank-slate quality. But he is far from blank. He has a roiling inner life, from the moment we meet him in The Matrix — surrounded by the detritus of his largely digital existence and with Massive Attack slinking from his headphones. As we watch him rebound from navigating a maze of cubicles with only the voice of a stranger as his guide to joyfully showcasing Yuen Woo-ping’s ecstatic fight choreography, we feel not only the wonder of this world the Wachowskis have created, but the joy of witnessing a star go supernova."

https://www.vulture.com/2019/02/what-the-matrix-predicted-about-life-in-2019.html

https://www.vulture.com/2019/02/the-matrix-was-when-the-wachowskis-ambition-went-mainstream.html

https://www.vulture.com/2019/02/15-irrefutable-reasons-we-might-be-living-in-a-simulation.html

https://www.vulture.com/2019/02/the-matrix-red-pill-internet-delusional-drug.html

https://www.vulture.com/2019/02/neo-stunt-double-on-how-the-matrix-changed-action-forever.html

https://www.vulture.com/2019/02/the-matrix-laid-the-template-for-the-modern-blockbuster.html

https://ascmag.com/articles/flashback-the-matrix

... and that's one of the many reasons I love Neo. the actor, too.

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https://www.thewrap.com/the-matrix-filmmakers-wanted-sandra-bullock-as-neo-before-keanu-reeves-took-the-role/

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new headcanon is that she plays Neo in another universe.

...imagine the crossover potential.

https://birthmoviesdeath.com/2019/03/28/would-the-matrix-be-a-hit-today

https://fashionista.com/2019/03/the-matrix-20th-anniversary-costumes

https://www.wired.com/story/the-matrix-legacy-book-excerpt/

https://www.hollywoodreporter.com/heat-vision/matrix-changed-hollywood-but-was-it-worse-1197779

https://variety.com/2019/film/columns/the-matrix-20-years-later-1203176896/

https://www.theatlantic.com/entertainment/archive/2019/03/the-matrix-movie-wachowskis-20th-anniversary/586084/

http://www.thedigitalbits.com/columns/history-legacy-showmanship/matrix-the-20th

https://uproxx.com/movies/fourth-matrix-movie-wachowskis/

and... no, it's not happening

https://www.slashfilm.com/the-matrix-reboot-wachowskis-chad-stahelski/

if anyone wants to (re)watch The Matrix in theater - AND has an AMC theater nearby - here's your opportunity...

(Unfortunately, not in my country :( )

https://www.slashfilm.com/new-matrix-movie-lilly-wachowski/

https://geekculture.co/wachowskis-not-involved-in-new-matrix-movie-but-hopes-it-is-better-than-original/

https://www.msn.com/en-us/movies/news/matrix-4-officially-a-go-with-keanu-reeves-carrie-anne-moss-and-lana-wachowski-exclusive/ar-AAG4X4G

https://variety.com/2019/film/news/matrix-4-keanu-reeves-carrie-anne-moss-lana-wachowski-1203307955/

https://deadline.com/2019/08/the-matrix-new-movie-keanu-reeves-lana-wachowski-writing-directing-1202674278/

https://www.slashfilm.com/the-matrix-concept-artists-the-matrix-4/

and even better
https://www.hollywoodreporter.com/behind-screen/braveheart-cinematographer-john-toll-boarding-matrix-4-1233871

They are profound, beautiful expressions of what makes is human and the nature of consciousness and love.

Just my opinion.