RE: 100 mile range!
I only use public charging points rarely, but I've had quite good experience it's the Polar instant app - you can download it to your phone/tablet straight away without having to wait for a card through the post. You have to put £20 credit on it but a lot of the locations are actually free, so I haven't actually used any of my credit up yet.
I wouldn't rely on being able to do 100 miles without some sort of Plan B but you might be OK if you could find somewhere for a 1.5 to 2 hour top up while you're having a coffee or something to eat to give you an extra 10-20 miles (all values very approximate indeed!).
Public charging points are a real minefield because of the different standards - for example hardly any of the Ecotricity points can be used by a Fluence as they have decided to concentrate on rapid charging.