How would that make it nonviable? The whole point of the gas motor in a Volt is to let you drive beyond battery range. Once you deplete the traction battery, you're essentially driving a standard hybrid that still gets excellent gas mileage and has similar range to standard gasoline cars. It's not like the i3 range extender where you lose substantial power once it kicks in, it has a microscopic fuel tank, and it's really just a last resort if the batteries can't get you where you're going.