Impedance testing for batteries is a non-intrusive way of preventing battery failure by identifying early signs of weakness or general deterioration in individual cells.
An AC current is applied to each battery through probes attached to the block terminals, with the internal impedance measured and recorded in milliohms. This broadly indicates the general condition the batteries are in, without placing any undue stress on their functionality.
Battery problems evolve over time and as they get older, their internal impedance increases until it reaches a manufacturer-defined threshold where replacement is recommended to reduce the likelihood of complete failure.
Regular impedance testing, every 6-to-12 months for example, enables you to build up a history of internal battery condition for every cell. Comparing batteries against each other makes it easier to accurately forecast end-of-working-life predictions and calculate when proactive replacement is necessary.
Impedance testing is non-intrusive, so can be undertaken in-situ on a live working battery system and completed in a few hours. As a comparison, another type of battery testing called battery discharge testing often requires operations to be shut down for several days at a time while the test takes place.
The main drawback of impedance testing is that it only gives a broad indication of the batteries' condition. For a more detailed analysis, more intrusive testing is required.