Cost? Less than a tank of premium gasoline. Tesla keeping hinting at about $50. Current swap time 2 minutes 58 seconds even with the additional protection plating. Robots will have to be tweaked but they think they can get total swap time down to 60 to 90 seconds. Each roboticized bay can carry up to 10 battery packs, sort of like a CD changer or jukebox. Rollout to major routes first, but designed to be adopted quickly as demand warrants. ie, factory built to standard pattern a knockdown kit, like the Superchargers themselves are.