The conclusion is obvious. To have an electric ship whose batteries and motors weighed no more than the fuel (about 5,000 tons) and the diesel engine (about 2,000 tons) in today’s large container vessels, we would need batteries with an energy density more than 10 times as high as today’s best Li-ion units. But that’s a tall order indeed: in the past 70 years, the energy density of the best commercial batteries hasn’t even quadrupled.
