6.6  Sodium-Sulphur (NaS)

• The NaS battery has nearly 4 times the energy/density of lead-acid batteries (a much smaller battery for the same power).
  
  
• Its main disadvantage is that it must be kept at 300 to 350ºC, requiring a built-in heater. Safety concerns have been raised.
  
  
• EVs that have used this type of battery include: Ford Ecostar.