rationalskepticism.org

This is an interesting link. Download the pdf file and look at the executive summary (pages 4 and 5). It shows the exponential growth of EVs as well as the exponential decline in battery costs. As of 2016 electric batteries are about 2/3 cheaper to produce than they were in 2010. This means a 100kWh battery costs around $30k now instead of roughly $100k a few years ago, and the trend is continuing. The energy density of batteries in increasing as well, meaning lighter / smaller / higher capacity battery packs.

http://www.iea.org/publications/freepublications/publication/global-ev-outlook-2016.html