If it is true that the steel confinement weighs about as much as one pax, and if the choice of lithium batteries over nicads is driven by weight, is there any net advantage for lithium?
Flightless, this is far from my area of expertise (and I haven't worked the 787), but my understanding at the time was they couldn't go back to nicads due to the energy density - basically a NiCad of sufficient storage capacity wouldn't fit in the available space.
I thought I read somewhere that Airbus was going to abandon Li batteries for the A350 after the Boeing problems - I wonder why they went back to Li (perhaps they ran into the same size issue?)