The changing demands of modern battery testers
In the past, one of the main purposes of a battery analyzer was to exercise and restore NiCd batteries affected by the “memory” effect. With today’s nickel-free batteries, however, memory is no longer a problem. Lithium-based batteries do not need a periodic discharge; these batteries cannot be restored through cycling when weak.
So, the modern battery analyzer has assumed some new duties. These include the priming of new batteries, performance verification through quick testing and energizing batteries that have fallen asleep due to deep discharge.
Common sense suggests that a new battery should always perform flawlessly, yet many packs fail to meet manufacturer’s specifications. With a battery analyzer, incoming batteries can be checked as part of quality control. Packs that perform poorly during the warranty period can be identified and returned for replacement.
The typical life of a Li-ion battery is 300 to 500 discharge/charge cycles or two to three years from time of manufacturing. The loss of battery capacity occurs gradually and often without the awareness of the user. The function of the battery analyzer is to identify weak batteries and weed them out before they become a problem. This task is especially pertinent in a fleet environment. The loss of adequate battery power is as detrimental as any other malfunction in the system.
Troubleshoot short run times
A battery analyzer can also troubleshoot a short run time. This is a common complaint, and multiple causes can contribute to this problem. In some instances, the battery may not be properly formatted when first put into service. Repeated cycling can correct this. Another problem is incomplete charge when charged with the original charger. A battery analyzer can help to compare the capacity when charged with the original charger, to the capacity when charged by the analyzer.
Another common cause of a short run time is high internal battery resistance brought on by use and aging. Many analyzers can measure the internal battery resistance. Some instruments can simulate the load signature drawn by a digital device to verify the run time according to load requirements.
Higher-than-specified power consumption is another reason for short run times. This, however, is mostly related to the way the equipment is being used.
Lithium-based batteries are sensitive to aging. If stored fully charged at elevated temperatures, the battery can deteriorate to 50% capacity in about one year. Similar performance degradations are observed on NiMH batteries when used under the same conditions. Although the battery is still considered new, the user will blame the equipment rather than the battery for poor performance. The analyzer can isolate such problems quickly and accurately.
With the increased dependence on battery power, the need for quick battery testing becomes apparent. Various test schemes have been introduced over the years, but none has caught on. Most have inherent problems with accuracy.
The battery needs to be fully charged before testing because different charge levels interfere with the state-of-health readings. Defense organizations invest heavily in quick battery testing, only to come up with textbook methods that require large computers that must build up extensive data banks of reference material for each battery type checked. In addition, the test time is often too long to be practical.
New techniques measure the state-of-health of a battery in three minutes. Cadex Electronics’ Quick-test is based on interference technology and uses battery-specific matrices that are derived through a “trend learning” process using artificial intelligence. The ability to self-learn enables the system to adapt to new battery chemistries without having to change hardware.
These new techniques can accommodate Li-ion, NiMH, NiCd and lead-acid batteries; the required charge level is 20% to 90%. If outside this range, the analyzer automatically applies a brief charge or discharge. The charge level within this acceptable range does not affect the state-of-health readings.
The matrix obtained through the “learn” function is stored in the battery adapters that also contain the battery parameters to configure the analyzer. One “learn” cycle is the minimum requirement for developing a working matrix. Better results are achieved when learning several batteries with varying state-of-health conditions. Once attained, the matrix can be copied to other battery adapters. Testing a battery with a properly learned matrix achieves an accuracy of 65% on most batteries.
With quick testing, customer service staff can examine batteries at point of sales. Service centers can quickly separate serviceable batteries from those that exhibit genuine defects. A full maintenance program may be needed to repair those batteries that are serviceable.
A common Li-ion battery failure is caused by excessive low discharge. This deactivates the internal safety circuit, and the battery appears dead. Modern analyzers can apply a gentle current to energize the battery. (Cadex calls this function “boost.”) Once the voltage reaches charging range, a full-service program verifies the battery.
To judge the effectiveness of this program, Cadex tested a large number of supposedly dead Li-ion polymer batteries from various manufacturers. When first measured, these batteries had no voltage and appeared dead. Charging the packs in their respective chargers was unsuccessful. After “boosting,” most batteries accepted normal charge. The analyzer applied a full-service program and attained capacities of 80% and higher in most batteries. All restored packs performed flawlessly when returned to service.
Boosting Lithium-based batteries is safe. However, if the cell voltage has fallen to 1.5V and has dwelled in that state for several days, a recharge should be avoided. A deep discharge may form copper shunts in the cells, which can develop an electrical short. The analyzers are supposed to identify such faults and terminate service.
Nickel-based batteries can also benefit from the “boost” program. Older batteries or those with advanced cycle count exhibit high self-discharge, a condition that cannot be corrected. If activated with boost and left unattended, the battery may revert back to its former state.
Connecting batteries for testing has been a challenge for technicians and engineers alike. Many so-called “engineering specials” with springs and levers have appeared, only to disappear because of impracticality. This problem can be solved with a flexible adapter.
A flexible-arm adapter accommodates virtually any battery type. By lowering the two arms fitted with contact probes, narrow and awkwardly placed contacts can be reached. Magnetic guides keep the battery in any position, horizontally or vertically.
The flex-arm adapter requires setting the battery chemistry, voltage and mAh rating. The edit key on the battery analyzer prompts the user to enter the specifications. The battery setting is stored in the arm.
To check batteries with quick testing, a common matrix may be used for packs that have similar chemistry, voltage and capacity rating. This applies to cellphone batteries consisting of a single Li-ion cell. If the readings are inaccurate, a separate matrix will be required for these batteries.
The flexible-arm adapter is best suited for technicians dealing with constantly changing batteries. However, large groups of identical batteries (fleet environment) are best served with custom adapters. These adapters are programmed at the factory and do not require setting of battery parameters.
With batteries flooding the market, the availability of suitable equipment to test them may outpace battery production. This void is especially apparent in the mobile phone market, where large quantities of batteries are being returned under warranty. Many of these presumably faulty packs are discarded without checking or attempting to restore them. In the end, the customer will pay with higher prices.
Testing and restoring batteries has become a complex assignment. Battery analyzers must be simple to operate and must also allow customer service staff to perform the task without much training. Properly used, these instruments will assist in managing the influx of returned batteries. The quick-test feature can sort packs that are serviceable from those that exhibit genuine defects.
Battery testing also serves public safety organizations, rental outfits and defense organizations. With the quick-test feature, a battery can be examined prior to releasing to a customer or assignment for a critical mission. Testing by applying a full charge and discharge cycle is impractical. Being able to verify battery performance on the fly, only those packs that are fit for the job are released.
Buchmann is the founder and chief executive of Cadex Electronics, Richmond, British Columbia, Canada.
This article contains excerpts from the second edition book, Batteries in a Portable World — A Handbook on Rechargeable Batteries for Non-Engineers. The 300-page book is available from Cadex Electronics through [email protected], or 604-231-7777 or most bookstores. For additional information on battery technology visit www.buchmann.ca.