An electrochemical impedance spectroscopy (EIS) circuit for measuring impedance of one or more electrochemical cells, comprising: an electrical energy storage device (ES); a first current regulator (CR1) connected between the electrical energy storage device and the one or more electrochemical cells; and a second current regulator (CR2), wherein power flowing into the first and second current regulators is decoupled, characterized in that either: (i) the first current regulator is connected in series with the one or more electrochemical cells; the electrical energy storage device is connected in parallel with the series connection of the first current regulator and the one or more electrochemical cells; and the second current regulator is connected in parallel with the electrical energy storage device, and with the series connection of the first current regulator and the one or more electrochemical cells; or: (ii) the first current regulator is connected in series with the electrical energy storage device; the series connection of the first current regulator and the electrical energy storage device is connected in parallel with the one or more electrochemical cells; and the second current regulator is connected in parallel with the series connection of the first current regulator and the electrical energy storage device, and with the one or more electrochemical cells. an electrical energy storage device (ES); a first current regulator (CR1) connected between the electrical energy storage device and the one or more electrochemical cells; and a second current regulator (CR2), wherein power flowing into the first and second current regulators is decoupled, characterized in that either: (i) the first current regulator is connected in series with the one or more electrochemical cells; the electrical energy storage device is connected in parallel with the series connection of the first current regulator and the one or more electrochemical cells; and the second current regulator is connected in parallel with the electrical energy storage device, and with the series connection of the first current regulator and the one or more electrochemical cells; (i) the first current regulator is connected in series with the one or more electrochemical cells; the electrical energy storage device is connected in parallel with the series connection of the first current regulator and the one or more electrochemical cells; and the second current regulator is connected in parallel with the electrical energy storage device, and with the series connection of the first current regulator and the one or more electrochemical cells; the electrical energy storage device is connected in parallel with the series connection of the first current regulator and the one or more electrochemical cells; and the second current regulator is connected in parallel with the electrical energy storage device, and with the series connection of the first current regulator and the one or more electrochemical cells; or: (ii) the first current regulator is connected in series with the electrical energy storage device; the series connection of the first current regulator and the electrical energy storage device is connected in parallel with the one or more electrochemical cells; and the second current regulator is connected in parallel with the series connection of the first current regulator and the electrical energy storage device, and with the one or more electrochemical cells. (ii) the first current regulator is connected in series with the electrical energy storage device; the series connection of the first current regulator and the electrical energy storage device is connected in parallel with the one or more electrochemical cells; and the second current regulator is connected in parallel with the series connection of the first current regulator and the electrical energy storage device, and with the one or more electrochemical cells. <EOS>