Two 100kWmin−1 (1.67kWh−1) Li-ion battery energy storage systems (BESS) are described. The systems include a high-power Li-ion battery and a 100kW power conditioning system (PCS). The battery consists of 12 modules of 12 series-connected Saft Li-ion VL30P cells. The stored energy of the battery ranges from 1.67 to 14kWh−1 and has an operating voltage window of 515–405V (dc). Two complete systems were designed, built and successfully passed factory acceptance testing after which each was deployed in a field demonstration. The first demonstration used the system to supplement distributed microturbine generation and to provide load following capability. The system was run at its rated power level for 3min, which exceeded the battery design goal by a factor of 3. The second demonstration used another system as a stand-alone uninterrupted power supply (UPS). The system was available (online) for 1146h and ran for over 2min.