Rocket Lab's Electron rocket actually does this with the batteries that power its electric turbo pumps. > The electric pumps are powered by lithium-polymer bat

Rocket Lab's Electron rocket actually does this with the batteries that power its electric turbo pumps. > The electric pumps are powered by lithium-polymer batteries. The second stage uses three batteries which are "hot swapped", two of the batteries are jettisoned once depleted to shed mass. https://en.wikipedia.org/wiki/Rocket_Lab_Electron https://en.wikipedia.org/wiki/Rocket_Lab_Electron