We already know the base price of the 2015 BMW i3 electric vehicle, and now we know the cost of the i3's optional range extender engine. (automobilemag.com)
A 2.4 - gallon fuel tank accompanies the optional range extender engine. (automobilemag.com)
A Nissan Leaf, for comparison is capable of up to 107 miles on a 30kWh battery (by EPA standards), while the EPA range for a BMW i3 with the optional range extender is 180 miles. (evo.co.uk)