I have a new 2017 Volt and I know that the battery capacity is 18.4 KWH. However, when I check the info screen that provides details "since last full charge", I've noticed that it never has gotten close to 18.4 KWH used, even when run from fully charged to fully discharged. It usually sits around 14.something KWH used. Does this sound accurate? Does the Volt have ~4 KWH of charge when "fully" discharged?