Battery technology will definitely need to improve before any system is practical enough to build and add to a fleet. I think there are power system assumptions

Battery technology will definitely need to improve before any system is practical enough to build and add to a fleet. I think there are power system assumptions being made regarding mid to far term viability of metal air batteries. Currently, they are expected in operation to be much closer to the 40 MJ/kg figure than existing battery technology: https://en.wikipedia.org/wiki/Metal%E2%80%93air_electrochemical_cell https://en.wikipedia.org/wiki/Metal%E2%80%93air_electrochemi... That said, what becomes really interesting (and tricky) is that these types of batteries actually get heavier as they discharge, which throws off intuition for optimal trajectory analysis. We're used to thinking in terms of planes getting lighter as they consume their fuel...