How well do batteries compare to human energy storage in fat?

Both fat and glugose have more than order of magnitude better energy density (both MJ/kg and MJ/litre).

Human metabolic efficiency for mechanical work is about 22-25% (measured on a bike) and about 80% efficient in intake (food -> fat). If you take that into account human energy storage is still several times better.

So, logically, the robots will use us for batteries.

I think I saw that in a movie..

I just hauled 220 lbs up and down 3,000 feet in elevation over 10 horizontal miles and could not perceive the least bit of fat reduction. :-)

Imagine if we had a device to charge our cell phones from our fat.