David Buchko, BMW advanced powertrain and heritage communications, told AutoblogGreen that:
The exact, official electric range of the i3 has not yet been announced. Speaking to Automotive News Europe, Maximilian Kellner, head of product management of BMW i division, said, "The i3 has a range on a single electrical charge of 130 to 160 kilometers [81-100 miles], but with two eco modes the EV range could grow to 220 kilometers [137 miles]."
The i3 range extender is meant to enable the car to go a little further than the pure BEV on those rare occasions when driver needs to go a little further. It is not intended for daily use. We've said that the REx [range extender] will double the effective range of 80-100 miles. I have not seen anything to suggest that it would not be capable of doing so.
If you've been eying the i3 and its best-of-both-worlds powertrain, now you've got a bit more information to go on as you plan your purchase. The i3 launches later this year.