Should you Measure Battery Conductance or Resistance to Monitor Battery Health?

Interview conducted by Jake WilkinsonDec 22 2016

The resistance and conductance of a battery are two parameters that can be used to determine the health of battery strings and identify failed cells. As the two different values have a such a close relationship to each other many battery users believe that the choice between measuring either conductance or resistance makes little difference - however, this is not the case.

AZoM spoke to Wayne Eaton, of Storage Battery Systems (SBS), about the advantages of measuring resistance, rather than conductance, and the benefits of using SBS equipment for resistance measurement.

Let’s start with the basics, what is a battery’s internal resistance and conductance? What is the difference between the two?

Internal resistance is the battery’s opposition to current flow. Conductance is a battery’s allowance of current flow.  Both are Ohmic measurements taken, recorded and used to diagnose or determine battery state of health.

A batteries internal resistance and conductance are inversely proportional to one-another - as one rises the other falls. shutterstock.com | Mrs_ya

Are there target ranges for a battery internal resistance and conductance?

Battery manufacturers have documented reference values for their product lines’ internal resistance values. Some manufacturers publish these in catalogues or cut sheets, while others provide upon request. To identify a baseline for a particular string, I recommend testing internal resistance or conductance immediately after purchasing the batteries.

How does the internal resistance and conductance change over the course of a battery’s lifetime?

Over the life of a battery, internal resistance will increase as the positive plates age, undergo grid corrosion and lose active material.  Conversely, as a battery ages, conductance values decrease as the battery becomes more resistive to current flow.

There are many factors that affect a battery’s internal resistance or conductance. These include: state of charge, temperature, sulfation of plates, dry out of cell electrolyte, etc.  Ohmic measurements can indicate these changes, but cannot identify specifically which changes are occurring.

What measures, if any, can be taken to help prevent these processes from occurring?

Maintaining the most critical parameters of a battery, including optimal charge and temperature control, can help maximize the service life.  

Most early battery failures can be eliminated by the proper control of these factors, in conjunction with a consistent and thorough maintenance program.

shutterstock.com | optimarc

How do internal resistance and conductance readings help identify a bad cell? What else can these readings identify?

A significant change from normal readings or the manufacturer’s reference value indicates an abnormality with the battery and additional investigation is required. While manufacturers do publish reference values, trending actual readings will help decipher what is normal for a battery and battery string.

Internal resistance readings can also help identify problems with inter-cell connections, corrosion of terminals and loose connection hardware.

Why do you believe that measuring internal resistance, rather than conductance, is a more effective way of monitoring battery health?

Internal resistance is an increasing characteristic and its age curve moves towards an infinite value. Conductance is a decreasing characteristic and its age curve moves towards a plateau of zero, because conductance readings can never be negative. Conductance readings with near zero baselines have little room for trending.

Some batteries have conductance measurements so low that readings may be impossible to take or differentiate. An internal resistance spike is always identifiable, but a conductance drop is not.

Are there any regulations that require battery users to take and report internal resistance readings and values?

IEEE-450, IEEE-1106, IEEE-1188, as well as NERC and FERC requirements all provide guidance on Ohmic testing and report retention as part of their maintenance activity recommendations or requirements.

shutterstock.com | optimarc

How often do you recommend testing the internal resistance of a battery string?

Personally, I suggest testing much more frequently than most regulations’ minimum requirements. A battery can fail at any time. A battery that tested normal today or a week ago could fail without warning if placed under a heavy load.

As an absolute minimum, each battery or cell should be tested on a quarterly basis. Anything beyond that is putting a battery system’s load at risk.

What measurements can the SBS-6500 Battery Analyser take to monitor battery health? How are these measurements processed?

The SBS-6500 Internal Resistance tester is designed to incorporate the entire history of multiple battery strings’ internal resistance, voltage and temperature readings.

This includes a complete historical value list with graphs for comparison and trending of every battery in every battery system. The information is stored on the SBS-6500, at the fingertips of the operating technician. A PC or diagnostic software isn’t necessary to view it.

What type of batteries can the SBS-6500 be used with?

The SBS-6500 can be used on any battery type of any chemistry or technology. With a range from 5-6000 amp hours, the SBS-6500 is a very user-friendly platform and maintenance tool in any battery related industry.

The SBS-6500 battery analyzer from Storage Battery Systems

What can battery temperature readings indicate?

Battery temperature measurements are also used to analyse health and performance.  Internal heating of the metallic components and high temperature readings can indicate problems such as cell failures, low acid levels and sediment collection.

How does the SBS-6500’s software assist your users for battery management? What other functionalities does the SBS-6500 Battery Analyser provide?

The SBS-6500 Software Suite (SBS Battery Link) is simple and easy to navigate. Setup of reference values and strings can be entered via the software prior to using the unit.

Built-in report generation and trending graphs assist with analysing data.  The “Exclusing” live monitoring feature allows users to capture and chart real time data while a battery or cell is under load.

The software provided with the SBS-6500 allows health trends in batteries to be identified and managed.

Where can our readers find out more about battery testing, the SBS-6500 Battery Analyser and Storage Battery Systems?

To learn more visit us at Storage Battery System’s website, attend one of our up-coming, free, Webinars or email us directly at [email protected].

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About Wayne Eaton

Wayne Eaton is the Technical Sales Engineer with Storage Battery Systems, LLC.  Since 1981 he has worked in the power generation, power distribution and data center environments, with a specialized focus on DC powered equipment, installation, maintenance, testing and training.

With an early start as a First Class Electrician aboard US Navy nuclear submarines and through various jobs with OEM’s and Equipment suppliers, Wayne advanced to application engineering and customer training across all of the critical power segments.

His diverse background and wide-ranging technical expertise plays a key role in development, testing and documentation of quality DC power products coming to market