In fact, the original script of The Matrix had the machines harvest humans to be used as ultra efficient compute nodes. Executive meddling led to the dumb battery idea .
I love their original idea. Having your brainpower sapped and also being part of a collective dream that creates the world around you is such a cooler and more philosophical idea.
not really. It's just different energy. Calories can be converted to a unit of heat, a unit of heat is directly analogous to a unit of energy. Electricity is a unit of energy as well. Thus you can compare them. It's how you compare things like electrical production efficiency of a thermal cycle generation process.