Those 4 kWh are split between upper and lower safety regions and a working buffer. To avoid damage/degradation of the pack, the car never charges to 100% or discharges to 0. In addition, the engine turns on before it reaches the very bottom of the part of the battery that ghee car will allow to be used - it holds the last kilowatt hour in reserve to use like a hybrid does in making the engine more efficient. This working buffer gives you a few miles on electric after the car runs out of gas, too.The 2016-17 Volt with a 18.4 KWH (total capacity) battery, when the Volt is driven in electric mode only 14-14.4 KWH are used so somewhere around 4 to 4.4 KWH are still in the battery when the Volt states there is no more electric range. Even when 0 miles for electric range is indicated the car will still pull electric from the battery in when it can replenish the electricity from the engiine to keep that 4-4 KWH reserve capacity in the battery.The Volt seems to have a mind of its own and will never let the battery drop to a certain level once the range indicator for electric displays 0 miles left.