Diagnostic Battery Management

Abstract

The super battery, when ready, will be incomplete without diagnostic management. Batteries have a defined lifespan; some die early, others may go with a bang. Tightening regulations will do little to improve performance and safety. Battery care begins by observing user-induced stress and aging symptoms. This paper introduces Diagnostic Battery Management (DBM); test methods that monitor the state-of-health (SoH) of a battery from work-force-to-retirement. DBM advances the battery to a reliable, safe, cost effective and environmentally sustainable travel companion.

A battery has the fundamental flaw of not knowing its performance. The outer appearance does not reveal its condition; a battery looks the same when fully charged or empty, new or old and in need of replacement. A car tire, in comparison, distorts when low on air and indicates end-of-life when the treads are worn. With the growing battery population and larger batteries packs, attention must shift to better diagnostics to improve reliability, improve safety and attain environmental sustainability.

Perhaps batteries are not given their due respect. Many engineers still treat the battery and charger as an afterthought in the long design process; for many the charger is seen as unnecessary baggage. In the 1970s, the world had computers but little software — shared software changed this. Today, the world revolves around the battery, but it lacks management. An industrial revolution in batteries is on the horizon.

Focus on Reliability and Sustained Growth

The battery is well suited for portable and wearable devices such as smartphones, laptops and pace makers. Fossil fuel with its polluting and noisy internal combustion engine (ICE) is reserved for heavy vehicles, airplanes and ocean-going ships. These two energy systems have little in common; competing against fossil fuel with a net calorific value that is 100 times higher than the battery secures the strong position. Conversely, petroleum cannot match the battery that is clean, quiet and has an instantaneous start-up with the touch of a switch. An ICE in a mobile phone or as pace maker would be unthinkable.

With the advent of the electric vehicle, the battery is advancing into a field what was ICE territory. Similar intrusions are seen with boats and unmanned aerial vehicles (drones). Time will tell how far the battery can go in conquering new grounds, and this rests on the anticipated improvements that will be made. Isidor Buchmann, founder of Cadex and author of BatteryUniversity.com predicts that, “Every 1 percent improvement in battery performance will widen battery applications by 10 percent.”

The battery is increasingly being promoted as a green energy solution to liberate society from the dependency on fossil fuels. While this is a noble endeavor, the battery is not yet mature enough to fill this important role. Pushing the boundaries reminds us of its many limitations of being an electrochemical power source that is slow to fill, holds limited energy, runs for a time like a wind-up toy and has a relatively short life span before quitting without warning.

Capacity is the leading health indicator of a battery. It represents energy storage that governs the runtime and predicts the end of life when low. Other characteristics affecting battery health are internal resistance that limits the current, as well as self-discharge that hints to a mechanical defect when high. It is believed that elevated self-discharge is the precursor of Li-ion fires. Older nickel-based batteries also have high self-discharge but this is not known to compromise safety. The pack may only go flat overnight.

A common method to evaluate battery capacity is by coulomb counting. This goes back 250 years when Charles-Augustin de Coulomb established the Coulomb Rules. Coulomb counting provides capacity estimation by measuring in-and-outflowing energies. The readings are stored in the smart battery and correlate with capacity, but inaccuracies develop with random usage. Calibration or a deep discharge in the device with a full charge corrects the tracking error.

Batteries often include a fuel gauge to indicate the charge level. While this is useful to predict the remaining runtime, the capacity is not shown and the user will ask: “Charge of what?” The fuel gauge always shows 100 percent after a full charge, even if the capacity has faded to 50 percent. State-of-charge readings are only useful if the battery condition is known, as is the case with a personal battery. Charge does not mean “able.”

Manufacturers specify the runtime of a device with a perfect battery delivering 100 percent capacity. This condition is short-lived because of fading. Regulatory approvals are tough but once rubber stamped, officials wash their hands and pass all responsibilities to the user. Entering workforce-to-retirement requires battery diagnostics that monitors capacity loss, identifies anomalies and predicts when a battery should be replaced. These services are seldom done because suitable technologies are not readily available; nor can the battery be removed for lengthy testing.

Cadex has been studying battery health for over a decade by analyzing symptoms. This led to the development of algorithms to estimate battery capacity as part of rapid-testing. The algorithms are derived by scanning thousands of batteries at various state-of-health conditions and then developing a test procedure that takes a snapshot of the chemical battery for the purpose of evaluation.

Rapid-test developments form the building blocks for Diagnostic Battery Management. These algorithms can be integrated into battery chargers, analyzers and monitoring devices. Test results can be shown on the charger and stored in a web-based application called Battery Embassy. Each service updates the status to provide real-time supervision as part of quality control and risk management in batteries.

A database requires a reference and the serial number in a smart battery serves as embedded ID. With test data on hand, the fleet supervisor can now do budgetary queries by calling up batteries with capacities below 80 percent for replacement.

Why Diagnostic Battery Management is Needed

To assure reliability, device manufacturers often mandate battery replacement by a fixed date stamp. In order to accommodate batteries with low and high usage, a two-year replacement is commanded. While simple, operation is cost-prohibitive and burdens the environment as most batteries are replaced prematurely. A quality Li-ion battery is good for 5 years typically.

Bio-med technicians have discovered that the capacity of most batteries in medical instruments is still above 90% when the date stamp expires. Dr. Imre Gyuk, Energy Storage Program Manager of the U.S. Department of Energy, reported that “every year roughly one million usable lithium-ion batteries are sent for recycling.”

As wasteful as the two-year data stamp policy may appear, it does not solve the battery problem. A U.S. Food and Drug Administration (FDA) survey says that, “up to 50 percent of service calls in hospitals surveyed relate to battery issues.” Healthcare professionals at AAMI (Association for the Advancement of Medical Instruments) report “battery management emerged as a top 10 medical device challenge.” A battery seminar that was organized by the FDA to improve battery reliability in healthcare came up with these concerns:

1. Insufficient quality assurance in medical batteries
2. Lack of knowledge integrating batteries in medical devices
3. Not knowing when to replace the battery

Summary and Objective

Battery users must become better custodians of this marvelous energy source. Developing a super battery is incomplete without addressing the problems identified by the FDA and other industries. With a predicted annual growth in battery usage of 20 percent, environmental concerns must also be addressed. This is where embedded diagnostics will play an important role. The ability to utilize each pack for its full potential lowers tonnage of batteries being discarded each year. Diagnostic Battery Management also improves system reliability and lowers operational costs.

We marvel about technological advancements but are less impressed with battery diagnostics. The battery still behaves like a “black box” with a mind of its own. In the near future, battery diagnostics will be built into chargers, analyzers and monitoring devices in the form of software running in the background and providing quality control in batteries. These advancements can be made economically and with minimal price premium. Industries benefitting from these developments are public safety, healthcare, defense, automotive, logistics, transportation and mining.

References

• FDA’s Antoinette Hazlett, manager of surveys, special studies, and research at the Center for Devices and Radiological Health (CDRH) Office of Surveillance and Biometrics, Division of Patient Safety Partnerships
• Battery management emerged as a top 10 medical device challenges in September 2014 AAMI News Release.
• Workshop to discuss battery issues in healthcare at FDA Headquarters in Silver Spring, Maryland, in April 2013

About the Author

Isidor Buchmann is the founder and CEO of Cadex Electronics Inc. For three decades, Buchmann has studied the behavior of rechargeable batteries in practical, everyday applications, has written award-winning articles including the best-selling book “Batteries in a Portable World,” now in its fourth edition. Cadex specializes in the design and manufacturing of battery chargers, analyzers and monitoring devices. For more information on batteries, visit www.batteryuniversity.com; product information is on www.cadex.com.