The usability of electrical vehicles strongly depends on performance, safety and lifetime of the utilized energy storage system. A typical lithium-ion battery system is supervised by a battery management system (BMS) to optimize operation and ensure safety over its whole lifecycle. Advanced BMS apply active charge balancing. In future, even more sophisticated approaches will be implemented like impedance spectroscopy based on driving current stimulation for online estimation of the energy storage’s state of health. For efficient development and testing of such BMS it is impractical to use real lithium-ion cells in arbitrary condition of state of charge, temperature and state of health. Consequently, hardware in the loop cell emulators are state of the art. In this paper, a novel modular wide bandwidth high performance lithium-ion cell emulator is introduced. The performance is proven by applying a commercial active cell balancing system and by performing impedance spectroscopy. One electronic unit emulates a single cell, while multiple units can be stacked to form a complete energy storage system up to 1000 V. Every module is autonomously operating in stand-alone mode and contains the full computing power for emulating open circuit voltage and output impedance depending on state of charge, temperature and aging. A fast high resolution acquisition stage samples the current with 18 bit at 5 Msps. The cell voltage is generated by a power amplifier with 8 MHz bandwidth and up to 10 A output current, while the output is fully protected. Leakage current can be measured down to 1 uA. High performance and long term stability is achieved by a self calibrating system, using a single stable floating zener reference.