An energy storage system is provided. The system includes an energy storage device including at least one battery module, a power adjuster that adjusts power of the energy storage device, a controller that controls the energy storage device and the power adjuster, a rack that accommodates the energy storage device, the power adjuster and the controller, the rack including at least one stationary coupler fixed to a movable unit and at least one support device that supports the energy storage system against the moveable unit.