[NeilBlanchard]

A serial hybrid without batteries is similar to the Volt. It is not an efficient way to do it, because you have to vary the RPM's and you need to be able to meet the *peak* power required, rather than just the average. And you have to run the ICE all the time, instead of about half of the time (or less).

So you have to increase the power of the ICE, and therefore you lose the main advantages of a serial hybrid has.