DABEL5
Why Molten Metal, Not Batteries
A Dyson module is a solar thermal power plant — store heat directly as molten Fe-Ni in zero-g. ~145 Wh/kg with latent heat, infinite cycles, all from asteroid ore.
ESS
Why Iron-Nickel Batteries, Not Lithium-Ion
There's no lithium on asteroids, you can't swap batteries every 10 years in space, and you can't put out a fire in vacuum. Iron-nickel batteries are made from asteroid smelting byproducts, last 30-50 years, and after full charge they produce hydrogen and oxygen.