From Green car congress,
"GM tweaks battery materials, pack size, SOC window to increase 2013 Chevrolet Volt EV range to 38 miles
7 June 2012
The all-electric vehicle range of the 2013 Chevrolet Volt will increase by three miles from the 2012 model to be 38 miles on a single charge. The miles per gallon equivalent (MPGe) fuel economy will increase from 94 miles to 98 miles and the total range, including extended range operation, will be 380 miles. Power consumption in EV mode is EPA-rated at 35 kWh/100 miles for the 2013 model, down from 36 kWh in the 2012 model."