Sodium Sulphur batteries offer very high performance. Power and energy weight densities are some three times that of lead-acid batteries. This is discussed in light of the recent transition this technology has made from laboratory devices to well integrated batteries running a small fleet of demonstration vehicles in Europe, USA, and Canada. Battery performance has not approached cell performance until recently, but with rapid advances in battery design we are seeing longer battery life. This is achieved by correctly designing and integrating the important sub-systems in the battery: the thermal control system, the cell array, the cell bypass devices and the safety devices. Energy, power and life data is presented for the current battery design.