BMW CEO Ludwig Willisch has said that BMW of North America will equip its initial US shipment of i3 electric vehicles with the optional gasoline range extender. With the range extender (vehicles equipped with it are dubbed BMW i3 Rex), the i3’s range nearly doubles to 200 miles before the electric car needs to find a charging station.

Unlike the Chevy Volt, the i3 range extender does not produce enough power to move the vehicle. “All it does is charge the battery and it typically kicks in only if the battery is discharged,” said Willisch. The i3’s performance will be affected when using the range extender. He went on to say it won’t be as agile and it won’t have full power when it is running the generator. The gasoline engine will be housed in the trunk and connected to a generator that recharges the battery, but will not transmit mechanical power directly to the wheels.

Although the BMW i3 Rex is optional, BMW expects up to 80% of buyers to go for it. Prices for the BMW i3 and the range extender  have not been announced, but it is expected to be in the mid $40,000 range.

The BMW i3 goes on sale later this year in the US, but BMW says there won’t be a significant number of them in dealerships until early 2014. Jacob Harb, head of electric vehicles and strategy for BMW, said service and technical dealership employees will be trained on how to service and repair the i3 and the i8 hybrid sports car in the second half of the year. BMW already has 64 dealerships capable of servicing electric vehicles, and they are the dealerships that are currently servicing the ActiveE trial vehicles.

This announcement comes on the heels of some recent spy shots showing the production BMW i3 with less camouflage, revealing the roofline and curve along the top of the windows. Looks like the BMW i3 has the floating-roof-look at the back like some of the new Land Rovers.