Thank you - yes, the battery capacity seems to be (as with most things) the limiting factor. For example the new 2018 Nissan Leaf has a 50KWh battery, which although better than the original Leaf battery of up to 40, it's hardly ground-breaking. I know Tesla are bringing out much bigger batteries, but that's not this year.
The 2019 models may be able to get up to 300 miles per charge, which would be very practical.
Tesla are AMAZING, from a petrolhead!