Battery Impedance Testing

The internal resistance of a battery is made up of two components: electrical, or ohmic, resistance and ionic resistance. Electrical Resistance is a measure of the opposition to current flow in an electrical circuit whereas ionic resistance is a measure of opposition to current flow due to internal factors such as electrode surface area and electrolyte conductivity.

Internal ohmic values (AC resistance) can be useful as a trending tool and can help to indicate the overall health of a battery being measured.

A lower internal resistance generally indicates a higher capacity; therefore, an increase in internal resistance over time can indicate declining battery capacity, or degradation. Measuring the trend over time will indicate which cells are weakest, or abnormal. It is important to note, however, that internal resistance varies between different batteries and battery manufacturers.

Replacing a whole battery string is a costly exercise. A preventative annual UPS battery impedance check will test each individual cell within the string. This can identify any weak or failing individual unit, leading to a much lower replacement cost (or possibly the battery being re-conditioned) compared to the expense of swapping out an entire string. At the same time this will of course check the overall battery string health ensuring that any UPS will deliver the protection expected from it when needed.