The metaphorical rocket equation's worse for batteries than for gasoline, since they don't get appreciably lighter as the energy is used up, whereas with a gas

The metaphorical rocket equation's worse for batteries than for gasoline, since they don't get appreciably lighter as the energy is used up, whereas with a gas engine you can throw the spent fuel out into the atmosphere for someone else to deal with. The rocket equation's only metaphorical here because the rocket equation's tyranny is really about how much reaction mass you have to carry, not so much the energy store. Chemical rockets kill two birds with one stone by extracting energy from fuel+oxidizer then using the waste products as reaction mass. But you can go with a nuclear powered rocket that gets all its energy from uranium and just uses plain water or something as reaction mass. The rocket equation's 'tyranny' is that your rocket constantly has to accelerate the reaction mass it plans to use later. Cars - electric or gasoline - do not require any reaction mass, though.