As a new I3 owner myself, I went through this tortuous process a month or so ago. As I live in the Midlands, I purchased a Plugged In Midlands Card at £24. I could have got the same access with a Source East Card at £10 (it also covers Source London). I also signed up to Polar Credit, CYC (£20) and Ecotricity (free). A lot of the local Councils seem to be moving from Plugged In Midlands to CYC. So far, I have used the Ecotricity card on a Rapid, and the Plugged In Midlands card locally as there are 6 by 7kW chargers sitting idle in a nearby carpark. As the latter are free to use, the car can get a top up whilst my wife and I in the local supermarket/library. I will re-visit the question of cards when they next come up for renewal.