 The Volt operates as a pure battery electric vehicle until its battery capacity drops to a predetermined threshold from full charge . From there its internal combustion engine powers an electric generator to extend the vehicle 's range as needed . When the engine is running it may be periodically mechanically linked ( by a clutch ) to a planetary gear set , and hence the output drive axle , to improve energy efficiency . The Volt 's regenerative braking also contributes to the on @-@ board electricity generation . Under the United States Environmental Protection Agency ( EPA ) cycle , the 2013 / 15 model year Volt all @-@ electric range is 38 mi ( 61 km ) , with a combined electric mode / gasoline @-@ only rating of 62 mpg @-@ US ( 3 @.@ 8 L / 100 km ; 74 mpg @-@ imp ) equivalent ( MPG @-@ equivalent ) . 
