I drive my i3 REX since August 2014.
In more than 70.000 km I tested the car (and the REX) in all kind of situations, and I think I know pretty well what I can expect. Honestly, I truly believe this is an amazing car, practically with no limits (if only the REX could offer a little more power and the tank a little more capacity, but this is another matter).
Not a single a problem so far, except the following, which appeared for the first time a few months ago (about at 60.000 km).
Highway on the plain, speed around 120 kmh, battery goes under 5% (approx.) and the REX turns on.
For 15-20 minutes the car slows down to a speed as low as 35 kmh up to 70 kmh maximum.
Then it can accelerate again even to the top speed, if the battery still has some juice.
Never had this problem before: the car always could (and still can) run at least at 120 kmh even when the battery goes to zero (except during those 15-20 minutes).
I would think to the ageing of the battery but what makes me really puzzled is that this happens only if the gasoline tank is full !
Same pattern, but with the tank at 3/4 and the problem doesn't occur.
In fact, the only thing that changes in those 15-20 minutes, is the fact the tank progessively empties from full to 3/4 (approx.)
Moreover, if I stop to refuel and resume the trip with the battery still very low (obviously) the problem doesn't occur a second time.
Here a you can see a few pictures of what the display shows when the condition is "active":
https://drive.google.com/drive/folders/ ... NNq0b3Pwb5
Local service has already checked the car and got in touch with the country headquarter's engineers but all they could offer are a few silly explanations that do not explain the observed behavior.