Comment by Hamuko

I don't think the fuel tank and gearbox in my car take up that much space when compared to the batteries in a Leaf or a Tesla. And you still need to put this where the engine used to go, so it's really a limited amount of space there as well.

Just for reference, this is the fuel tank in my car: https://traversparts.com/download/normal/246883_1.jpeg

And this illustrates where the batteries in a Leaf are: https://s1.cdn.autoevolution.com/images/news/nissan-leaf-bat...