Built upon real-world supervisory control and data acquisition (SCADA) and other measurements of a featured utility-scale testbed, this paper addresses the participation of customer side battery energy storage in providing peak load shaving at a 12.47 kV distribution feeder. A stochastic optimization-based battery operation framework is developed that enables feeder load peak shaving under offline (day-ahead) as well as online (close-to-real-time) control settings. Both designs work through establishing a secured communications line to the utility’s feeder-level SCADA system. Multiple field experiments are conducted, including a full day test with complete control of a 1 MWh/200 kW battery system, as well as various numerical assessments based upon one year of real feeder data.