[William Tell]

-YYZ- said: "...why would it only about double the range of electric cars using it?"

One possibility might be that the new design is significantly heavier than the old design and can't be scaled down. You might end up with additional range but carrying a much heavier payload.

[glorgau]

..why would it only about double the range of electric cars using it?"

Because people will be able use the heater or air conditioning.