I would think even lower than that, but I don't fully disagree with X-Traction. My problem is, especially on the highway, that I often am "charging" an already full battery. Then when I'm in traffic, I'm depleting the battery rather quickly.
the A1 e-tron was pretty cool in that it used a tiny rotary as the generator power plant, minimizing weight.
So I read an article today about the Mazda 2 range-extended electric (similar to the Volt's powertrain). If that's what you were referring to, or if the A1 used the same layout, then yes, that is pretty cool. Mazda claims that because the rotary will only be spinning at 2,000rpm (its highest efficiency zone) to generate (and never more/less), then it ends up being just as efficient as a petrol, but weighing far, far less. If their claims aren't completely bogus, then that's a really, really neat application of the rotary. Shame there are no plans to mass-produce it. Imagine a plug-in BEV with that range extender - would make a fuel cell almost completely moot - only downside is that since it's still burning petrol, it will have emissions. Still, the temperature and infrastructure limitations make me think that fuel cells will never take off. The only positive I see about fuel cell tech is that producing the hydrogen required can be a really, really efficient process when coupled to recycling plants, algae ponds, or using excess energy that is otherwise given away (Ontario pays neighbouring states/provinces to take our excess electricity during low times) or grounded.
Still, I think the best gains will come from new battery tech. Imagine a Tesla Model S with a small range extender (rotary) in the 'frunk'. Now there's the perfect vehicle.