Keep in mind the Gen II Volt by EPA numbers is between 5% (hwy) to 12% (city) more efficient than the Gen I Volt.
Also on the Gen I Volt EV range usable battery was about: The unused battery on the Gen I Volt was 6KWh.
2011 - 2012 - 10KWh
2013 - 2014 - 10.5KWh
2015 - 11.1KWh