This is <i>not</i> the way most hybrids work.  Ford, honda and toyota vehicles have power-split or series parallel where the power delivery is some percent electric&#x2F;gas.  In other words most hybrid cars can drive 0 miles on electric only and require some combination of gas and electric power.<p>The series hybrid that you describe is available in the chevy volt and an option on the bmw i3 series.  The electric only range of these is 53 (volt) and 81 (i3) miles.  These are very much &quot;mostly electric&quot; cars.<p>Most hybrids, in split&#x2F;parallel mode, are essentially ICE cars, but with significantly improved gas mileage.  This significant improvement in gas mileage (going from ~30 mpg to ~50 mpg) is a good reason to include them, but it does mean a half-assed parallel battery power system could be used to game the system.<p>There should probably be some minimum torque delivery or percent power required.