The principle is basic and it's similar to the public bike rental services in Paris or Lyon, although at a smaller scale. 50 electric cars (converted Peugeot 106) distributed into 7 different stations throughout la ville.
It's a very simple and straightforward service, called Liselec. You first have to register and get a card. Then you simply get to one of the 7 stations (the service is available 24 hours a day, 7 days a week) and swipe your card and select a car with a green light at the back (which means it's ready). The cars have a small keyboard between the front seats where you have to type your personal access code. If you stop for something, click on A (so your shopping time doesn't count as rental time) and click on F once you are finished and park the vehicle.
The car registers all the trip data (distance, speed, time) and calculates the price. Once the car is back at the station, it transfers the information via modem which is then gathered and billed to the customers. The fares are very good. There's a basic monthly fee of 5.5 EUR (2 for students) to which you have to add your usage. For instance, 5 km (3 miles) cost 2 EUR.
[Source: La Rochelle town hall (link is in French)]