We can think of it from a different angle. let's say we have 2 cars, one is accelerating on a road from 0 to velocity V, the second accelerates on a platform until it reached a velocity V but the platform itself is also moving in velocity V, so the second car is actually reaching a velocity of 2V. if we measure the difference of the kinetic energy of each car before and after the acceleration, we will get that the difference in the kinetic energy of the second car is 3 times then the change in the first car, (0.5M(2V)^2 - 0.5MV^2 = 1.5MV^2). According to the book, the sconed car engine has 3 times the power of the first one, this is because we measuring energy according to the distance the object moves, if for example V=50, the average speed of the first car was 25, when the average speed of the sconed car is 75, so the second car does 3 times the distance that the first car does, also they both consume the same energy to do so. It of course not relevant to the type of engine or to exhaust etc. it's just the way we are measuring energy.

It seems that we can't just ask about the potential energy of a battery or a gallon of fuel, because it depends on the way we are using it. it basically can be any number. But we may ask instead about the Impuls size we can produce from it which will give us a straight answer.