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Battery Recovery Rate
Restoring batteries by applying controlled discharge/charge
cycles varies with chemistry type, cycle count, maintenance
practices and age of the battery. The best results are achieved
with NiCd. Typically 50 to 70 percent of discarded NiCd batteries
can be restored when using the exercise and recondition methods
of a Cadex battery analyzer or equivalent.
Not all batteries respond well to exercise and recondition.
An older battery may show low and inconsistent capacity readings.
Another battery may get worse with each advancing cycle. An
analogy can be made to a frail old man for whom exercise is
harmful. Such a condition suggests battery replacement.
Some older NiCd batteries recover to near original capacity
when serviced. Caution should be applied when rehiring these
old-timers because of possible high self-discharge. If in
doubt, measure the self-discharge. A 10 percent self-discharge
in the first 24 hours after charging is normal. Discard the
battery if the self-discharge approaches 30 percent.
The recovery rate of NiMH is about 40 percent. The lower yield
is in part due the reduced cycle life. Some batteries may
exhibit irreversible heat damage suffered by incorrect charging.
Elevated operating and storage temperatures also contribute
to permanent capacity loss.
Lithium-based batteries have a defined age limit. Once the
anticipated cycles have been delivered, no method exists to
restore them. The main reason for failure is high internal
resistance caused by oxidation. Operating the battery at elevated
temperatures will momentarily improve the performance. However,
the high internal resistance will revert to its former state
when the temperature normalizes.
Many Li-ion batteries for cell phones are being discarded
under the warranty return policy. Dealers have confirmed that
80 to 90 percent of these batteries can be repaired with a
battery analyzer. Because no equipment is on hand, the batteries
are often sent back to the manufacturers or are discarded
without attempting to restore them.
Some Li-ion batteries fall asleep if discharged below 2.5V/cell.
The internal safety circuit opens and the charger can no longer
service the battery. Advanced battery analyzers feature a
boost function to activate the protection circuit enabling
a recharge. If the cell voltage has fallen below 1.5V/cell
and has remained in that state for a few days, a recharge
should be avoided because of safety concerns.
The recovery rate for lead acid batteries is a low 15 percent.
The reasons for the low yield may be due to incorrect charging
methods, high cycle count, operating at elevated temperatures
and old age.
The question is often asked whether a restored battery will
work as well as a new one. The breakdown of the crystalline
formation on NiCd can be considered a full restoration. However,
the battery will revert back to its former state if the required
maintenance is denied. If the separator is damaged by excess
heat or is marred by uncontrolled crystalline formation, that
part of the battery will not improve.
Battery Test Equipment
Battery analyzers have become an important tool to test, exercise
and restore batteries. The Cadex 7400, for example, accommodates
NiCd, NiMH, Li-ion/polymer and lead acid batteries and is
programmable to a wide range of voltage and current settings.
A quick-test program measures battery state-of-health in three
minutes and a boost program reactivates dead batteries. There
is even a program to measure the battery self-discharge.
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Figure 2: Cadex 7400 battery analyzerThe programmable
four-station battery analyzer has a range of 1.2 to 16V
and 100mA to 4A. Each station operates independently.
Custom battery adapters simplify battery interface, universal
adapters accommodate less common batteries. Nickel-based
batteries are automatically reconditioned if the capacity
falls below the user-defined target capacity. |
Battery analyzers are capable of solving a multitude
of battery problems. Regular exercise doubles the service life
of NiCd and reduces replacement costs. Unserviceable batteries
are weeded out before they cause problems. Most importantly,
battery analyzers improve battery reliability, an issue that
is of significance in critical mission applications.
This article contains excerpts from the second edition book
entitled Batteries in a Portable World — A Handbook
on Rechargeable Batteries for Non-Engineers. In the book,
Mr. Buchmann evaluates the battery in everyday use and explains
their strength and weaknesses in laymen’s terms. The 300-page
book is available from Cadex Electronics Inc. through book@cadex.com, tel. 604-231-7777 or most bookstores.
About the Author
Isidor Buchmann is the founder and CEO of Cadex Electronics
Inc.in Vancouver, British Columbia, Canada. Mr. Buchmann has
a background in radio communications and has studied the behavior
of rechargeable batteries in practical, every day applications
for two decades. The author of many articles and books on
battery maintenance technology, Mr. Buchmann is a well-known
speaker who has delivered technical papers and presentations
at seminars and conferences around the world. He can be reached
at Tel: 604-231-7777; Fax: 604-2317755; E-mail: Isidor.Buchmann@cadex.com.
About the Company
Cadex Electronics Inc.
is a world leader in the design and manufacture of advanced
battery analyzers and chargers. Their award-winning products
are used to prolong battery life in wireless communications,
emergency services, mobile computing, avionics, biomedical,
broadcasting and defense. Cadex products are sold in over
100 countries.
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