Electric car sharing services have been growing in popularity in the last years but operators are striving to reduce the costs of deploying and managing their charging infrastructure. Charging technologies that offer power sharing have the potential to achieve this goal but at the cost of increasing management complexity. In order to address this problem, in this work we propose an efficient optimized charging methodology that minimizes recharging costs when power sharing is used and also takes into account customer satisfaction. To this aim, we formulate the recharging problem as a two-step optimization problem, considering a realistic energy pricing scheme, and we evaluate this solution using real traces of parking times in a French station-based car sharing system. We show that significant cost savings can be achieved without impacting customer satisfaction and also reducing the strain on the grid with respect to a baseline approach.