Does internal resistance reveal battery capacity?
Isidor Buchmann Cadex Electronics Inc. isidor.buchmann@cadex.com www.buchmann.ca June 2004During the last 20 years, three basic battery rapid test methods have emerged: DC load, AC conductance and multi-frequency electro-chemical impedance spectroscopy (EIS). All methods are resistance based, a characteristic that reveals the battery’s ability to deliver load current. Internal resistance provides useful information in detecting problems and indicating when a battery should be replaced. However, resistance alone does not provide a linear correlation to the battery’s capacity. The increase of cell resistance only relates to aging and provides some failure indications. When measuring the internal resistance of brand new VRLA cells from the same batch, variations of 8% are common. The manufacturing process and materials used are only two of many possible variables contributing to this variance. Rather than relying on an absolute resistance reading, service technicians take a snapshot of th
