As the number of plug-in electric vehicles (PEVs)increase, the need for public fast-charging stations intensifies. In such facilities, concurrent charging of several vehicles significantly increases demand charges and stress supporting network elements. In this paper, we propose a stochastic fast charging station model which accommodates PEV demand through power drawn from the grid and an on-site energy storage system. The latter is used to lower peak demand and improve grid reliability. The station is modeled by a 2-dimensional Markov chain and the performance is measured by outage probability. The proposed model allows the station operator to optimally provision system resources to provide a good quality of service to customers. Numerical results indicate significant gains in net profit and useful insights can be made with the right choice of storage size.