Let's Get Technical: September 2016

NiMH Battery Conditioning: A Very Misunderstood Topic in the Aftermarket Service Market - And It’s Time to Change It

Nickel Metal Hydride (NiMH) technology has been used in the automotive electric propulsion market since the early-1990’s, starting with Battery Electric Vehicle (BEV) applications (ex: GM EV1).  It was a welcomed replacement to the Advanced Lead Acid battery technology with offering an Energy Density that was double that of the lead acid technology.  As NiMH continued to mature it was utilized in the Hybrid Electric Vehicle (HEV) market for products such as the GM Tahoe/Yukon, Honda Civic, Ford Escape, Lexus RX400h, and Toyota Prius – to name a few.  Therefore, as the NiMH products increased in volume, there was a natural interest in high voltage battery pack rebuilding or remanufacturing in the Aftermarket as the vehicles were exiting the warranty period.  This led to hobbyists, “weekend warriors” and, do-it-yourselfer technicians rushing into the market to stake their claim for a profitable business venture in the rebuilding of HEV battery packs. 

However, as many of the hobbyists and others eventually learned, there is more to rebuilding battery packs than meets the eye.  There is significantly more to rebuilding these packs than reading an article, blog, or other posting on the internet on how to “condition” battery modules.  Most individuals are unaware that there is much more to analyzing, diagnosing, and rebuilding a NiMH battery pack than conditioning or what some refer to as reconditioning.  Professionals must consider Screening and where the vehicle has spent its service life.  The experiences of our company engineers at FutureTech is that most hobbyists and other individuals simply do not have the training, equipment, or experience to properly screen, condition, and rebuild a battery pack.  Field quantitative and qualitative data support this these assertions.  So, let’s take a look at some of the areas that expand past the mere conditioning of NiMH modules.

Conditioning
Conditioning is another word for “cycling” the battery pack.  Cycling is defined as discharging the battery pack/modules to 0% State-of-Charge (SOC) and charging the pack to 100% SOC.  Cycling the NiMH modules will increase the capacity of healthy modules and provide data so battery pack capacity can be increased and balanced.

Screening
Screening battery modules requires appropriate equipment, and professionally trained technicians using the equipment to acquire battery energy, power data and, discharge (curve) signatures that permits a trained technician to review all testing data and review the performance of a battery module or cell.  Screening is a component of the conditioning process and serves as the essential diagnostic point of the entire rebuilding process.  Screening is one of the most crucial steps in determining what treatment a battery will need while being rebuilt, whether only conditioning is necessary or if module/cell replacement is necessary. 

Testing Procedures    
Battery packs (modules or cells) require both Power and Energy (capacity) testing to ensure optimal performance.  Power and Energy are not the same values/quantities.  Most hobbyists, do-it-yourselfers, and others typically do not understand this difference.  Energy is “how much” energy can be stored (capacity) by a module or cell. Power is the rate in which the energy can be delivered.  As an analogy, if a battery module is a 55 gallon drum that stores water then, the amount of water it can store/hold is Energy (capacity). Power is how fast (rate) that the water can be removed from the drum.  Therefore, both quantities must be tested because, one of the quantities may be functioning properly while the other is not.  Battery modules can be Energy limited but, not Power limited – and vice-versa.  Both must be tested.

Vehicle Service Life
One of the areas that FutureTech engineers have tracked for over a decade is how the geographical area, terrain, drive cycle, and calendar aging variables effect how a battery pack will perform.  Based on where a vehicle is located geographically provides a strongly correlated indicator for determining battery pack longevity and performance.  Ditto for the terrain, how the vehicle is used (drive cycle), and the age of the battery pack.  Each variable has a weighted value when analyzing the Power and Energy test data.  When FutureTech trains battery technicians, we use all of these variables to assist the technician in how to interpret battery testing data and arrive at the correct diagnosis and action plan before rebuilding the battery pack.
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So, What Does This All Mean?
If your business plans to rebuild NiMH battery packs, it is imperative that you properly vet your equipment and training supplier before taking the plunge.  In FutureTech’s experience, seldom do suppliers within the automotive Aftermarket make it through the vetting process.  The supplier should have at a minimum vehicle manufacturer experience in the areas of electric propulsion, and high voltage battery pack systems in particular.  If you plan to purchase battery packs from a supplier that rebuilds, it is essential that you properly vet them to learn about their capabilities in testing and rebuilding battery packs before you make any commitments.

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NiMH Battery Conditioning: What it is and How it is used in conjunction with - but differs from - Battery Analysis and Screening

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Author

Dr. Mark Quarto
Chief Technical Officer
FutureTech Auto, LLC