As explained in the range article the usable hours of energy will be effected by how you drive your car, but it is however useful to know what all the numbers mean.

 The power capacity of your vehicles battery is measured in kWh (Kilo Watt Hours), which are units of usable energy (like litres in a fuel tank).

So a 100kWh battery (Tesla P100d) can store 100 kWh of usable energy. Therefore if you averaged 4 miles per kWh you would achieve 400 miles.

This is because in the above calculation each kWh will last for 4 miles. 

This makes the consumption figure (miles per kWh) a really important number to understand, because if you drive your Tesla P100D to work every day your range will be considerably different to spending the day at a racetrack. 

It is useful to understand that battery technology is still new and progressing every year. So how you drive and charge your vehicle depends on which car is right for you and what is true right now may not be in 6 months time.

Historically small cars have smaller fuel tanks because they tend to do less miles, this is the same as smaller electric vehicles that may have smaller 40 kWH or 60 kWh batteries.

 The battery capacity should be one of the biggest considerations when buying a new car, but having a 7kW charger at home will make a huge difference to life with an EV..

Click here for more information on chargers.