Apparatus and methods for testing electrochemical systems

An apparatus for testing an electrochemical system, the apparatus comprising:

• a testing module adapted to be electrically coupled to the electrochemical system, the testing module comprising a discharge circuit configured to draw time-varying test current from the electrochemical system wherein the time-varying test current comprises a combination of a plurality of waveforms having different frequencies, the combination comprising at last one of:
• a superposition of the plurality of waveforms of different frequencies and a sequence of the plurality of waveforms having different frequencies and to controllably vary a magnitude of the time-varying test current, wherein the discharge circuit is configured to draw the time-varying test current from the electrochemical system continuously during testing of the electrochemical system;
• a measurement module configured to measure terminal voltage across terminals of the electrochemical system and the test current drawn from the electrochemical system by the testing module;
• and
• a processor configured to:
• compensate the voltage measured by the measurement module to at least in part compensate for voltage drift caused by continuously drawing the time-varying test current comprising the combination of the plurality of waveforms having different frequencies from the electrochemical system;
• and
• compute a state of health of the electrochemical system based at least in part on the compensated voltage and the measured current.