Well it sounds like it gets roughly 50mpg when it's running the generator to replenish the batteries as they are used up...really what they need to do is see what it gets in the city and highway (current EPA tests) but in mi/watthour (or whatever). Then you get two pairs of results.
All-electric: range in the city (miles), range in the highway (miles)
After all-electric: city (mpg), highway (mpg)
That is the only way to get a complete picture. It won't be as cool sounding as 230mpg, but that's really misleading.
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