2x as many batteries would last 2x as long. Maybe longer when charged more slowly. I read about maybe the first electric ferry, that the grid could not supply

2x as many batteries would last 2x as long. Maybe longer when charged more slowly. I read about maybe the first electric ferry, that the grid could not supply the power demand when speed charging the ferry. A new power line with greater capacity was then build. Grid operations are generally better off with lower peak demands.