Apparently, instead of batteries the original idea was to have them be part of a brain based neural net which makes a lot more sense than batteries. But this was felt to be too complicated.
If the machines from the Matrix needed to use some mammals as batteries, why not just use cows instead of humans? They'd be much more complacent with living in the Matrix, grazing on virtual fields, and less likely to wise up and try to escape and rebel against the machines since they're not very intelligent and the machines would need a lot less processing power to simulate a realistic cow world than the world in 1999 for humans.
To wit, if someone has access to a lot of GPU compute, could you please use gen-AI to re-make the Matrix but with the characters as cows, I'd pay to watch it. Would definitely beat Matrix Resurrections or whatever that cash grab turd was called.
Of course that means anyone unplugged from the Matrix would immediately become an S-tier genius. And how the hell do you write that?