Nowadays, big cities have to face transportation problems which are crucial for their survival. One of the solutions that is currently spreading in developed countries is to put a pool of electric cars at the disposal of customers to make local journeys. In this kind of system, cars are parked in stations where their batteries are recharged. A customer uses an electric car to travel from on station to another. Then, if necessary, the same customer will later use another electric car to travel to a third station, and so on. It is easy to understand that the gravity center of the set of cars changes during the day. This requires an action that consists in transporting cars from stations having excess of cars to stations that many run out of cars soon. Such an action is called a balancing action. The goal of this paper is to propose a balancing method that consists in using a truck of a given capacity. This truck visits the stations following a given circuit, and either leaves cars in stations when needed or takes cars from stations where they are in excess. Indeed, this method analyses the state of the whole system in order to make a decision at the arrival of the truck in a station.