The invention provides a battery performance assessment apparatus which includes two terminal connectors configured to electrically connect the assessment apparatus to the positive and negative terminals of a battery being assessed, and a response measurement system configured to measure the terminal voltage and current of the battery when supplied with at least one alternating test current having a frequency less than the impedance transition frequency associated with the battery being assessed and preferably between 100uHz and 1mHz, and a processor in communication with the response measurement system and being configured to output a performance assessment indicator for the battery being assessed by calculating at least one impedance for the battery using terminal voltage and current measurements communicated by the response measurement system.