A little of topic but the last reply mentioned a 8.5 KW generator would be capable of running the I-MiEV at 45 mph continuously. The problem with the "range extender" issue is how much power you really need to complete the task. On one hand the required source of extra power adds weight (and if external like a trailer) drag to the vehicle which increases the output requirement of the power source which adds more weight/drag. On the other hand, unless you really have a long journey, most people overestimate the size requirement of the additional power source. If you start out on the premise that you will have a full battery on departure and an empty battery on arrival at your destination, you can add the miles available from the pack to your range extender power requirement calculation. You only need to supply the battery with enough extra power to slow it's discharge rate so that it is depleted at your destination. Say you use a 3 KW generator to provide additional power. If you wanted to go through the trouble, it would fit in the back of the I-MiEV which only causes a weight increase and no additional drag. Because it is constantly putting 3 KW into the pack regardless of the load the vehicle is drawing, I think you would be surprised at how much range could be added. If there was no place to plug in at your destination, the generator could be allowed to run the entire time starting to add storage to the pack for your return trip.
Kind of a mind thing and a range anxiety reliever but not really practical. You would have to plumb the generator so it wouldn't kill you from carbon monoxide poisoning, listen to the noise, and burn fossil fuels. Then there is the cost of the generator itself. Much cheaper to use the EV for its intended purpose and rent an ICE vehicle for the times you need a long trip. Just to put it on my bucket list, I needed to take the Tesla from Florida to Michigan. Instead of shipping it, which would be the rational thing to do, I started out on a non-stop trip for 1400 miles. The trip that takes about 20 hours in a ICE vehicle took 28 hours in the Tesla which included nine supercharger stops. Fortunately, the stops allowed for some nap time which made the trip possible. It is doable but like a I-MiEV with a range extender, just not practical. And (just to get me sort of back to the thread title and not totally off topic) IMO, the I-MiEV's efficiency at highway speeds due to aerodynamic drag and it's high speed handling characteristics make it unsuitable for cross-country driving even if it had unlimited range. Based on its purchase cost and operational cost per mile, the I-MiEV is still the greatest and most practical vehicle in the world if you operate it within the limits of its intended purpose.