The present disclosure relates to methods and systems for management and control of interconnected energy storage modules, such as battery packs, that can form a larger energy storage system. The disclosure also relates to methods and system for the measurement of cell impedances in a battery pack in-situ and on-line and using active balancing circuits that may already be present in the battery pack. The methods and systems can inject disturbances of different frequencies and measure impedance by using the active balancing circuits present in the battery pack, which can transform an active balancer into a dual active balancer and impedance measurement system. The speed up of impedance measurement energy storage modules can be accomplished by using multi-tone, orthogonal or spread spectrum waveforms applied simultaneously on all or a sub-set of the active balancer circuits in an active balancer.