See Lithium-Sulphur which has a theoretical limit of ~2500 wh/kg vs ~250 wh/kg of todays lithium batteries. So you're looking at up 10x improvement, if we can g

See Lithium-Sulphur which has a theoretical limit of ~2500 wh/kg vs ~250 wh/kg of todays lithium batteries. So you're looking at up 10x improvement, if we can get to 1000 wh/kg that's your 4x. https://en.wikipedia.org/wiki/Lithium–sulfur_battery https://en.wikipedia.org/wiki/Lithium–sulfur_battery