[Blue Bomber Man]

Im sure that as long as you size the system appropriately that it would be energy efficient. Cost and return on investment are the real questions. With lith ion batteries plan on about $1000 per kwh, probably need about 2-3 kwh (prius has 7 i think). Weight for the batteries would only be around maybe 25 lbs per kwh (their gravimetric density is usually 150-250 w/gram)

A small motor/generator /w control unit would maybe be 75-100 pounds (I am ball parking all these numbers)

The real challenge would be in integrating it to a non-hybrid vehicle.

In another note, I am hoping to begin building my website soon that will track the progress of my car that I hope to build from scratch. I hope materials and batteries come down in the next year or two for when (if) I start building it =)