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Battery Recovery Rate
The battery recovery rate 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 device.
Not all batteries respond equally well to exercise
and recondition services. An older battery may show low and
inconsistent capacity readings with each cycle. Another will
get worse when additional cycles are applied. An analogy can
be made to a very old man for whom exercise is harmful. Such
conditions indicate instabilities caused by aging, suggesting
that this pack should be replaced. In fact, some users of
the Cadex analyzers use the recondition cycle as the acid
test. If the battery gets worse, there is strong evidence
that this battery would not perform well in the field. Applying
the acid test exposes the weak packs, which can no longer
hide behind their stronger peers.
Some older NiCd batteries recover to near original
capacity when serviced. Caution should be applied when ‘rehiring’
these old-timers because they may exhibit high self-discharge.
If in doubt, a self-discharge test should be carried out.
The recovery rate of the NiMH is about 40 percent.
This lower yield is, in part, due to the NiMH’s reduced cycle
count as compared to the NiCd. Some batteries may be afflicted
by heat damage that occurs during incorrect charging. This
deficiency cannot be corrected. Permanent loss of battery
capacity is also caused by prolonged storage at elevated temperatures.
The recovery rate for lead acid batteries is
a low 15 percent. Unlike nickel-based batteries, the
restoration of the SLA is not based on reversing crystalline
formation, but rather by reactivating the chemical process.
The reasons for low capacity readings are prolonged storage
at low terminal voltage, and poor charging methods. The battery
also fails due to age and high cycle count.
Lithium-based batteries have a defined age limit.
Once the anticipated cycles have been delivered, no method
exists to improve the battery. The main reason for failure
is high internal resistance caused by oxidation. Operating
the battery at elevated temperatures will momentarily reduce
this condition. When the temperature normalizes, the condition
of high internal resistance returns.
The speed of oxidation depends on the storage
temperature and the battery’s charge state. Keeping the battery
in a cool place can prolong its life. The Li-ion battery
should be stored at 40 percent rather than full-charge
state.
An increasing number of modern batteries fall
prey to the cut-off problem induced by a deep discharge. This
is especially evident on Li-ion batteries for mobile
phones. If discharged below 2.5V/cell, the internal protection
circuit often opens. Many chargers cannot apply a recharge
and the battery appears to be dead.
Some battery analyzers feature a boost, or wake-up
function, to activate the protection circuit and enable a
recharge if discharged too low. If the cell voltage has fallen
too low (1.5V/cell and lower) and has remained in that state
for a few days, a recharge should not be attempted because
of safety concerns on the cell(s).
It is often asked whether a restored battery
will work as good as a new one. The breakdown of the crystalline
formation can be considered a full restoration. However,
the crystalline formation will re-occur with time if the battery
is denied the required maintenance.
When the defective component of a machine is
replaced, only the replaced part is new; the rest of the machine
remains in the same condition. If the separator of a nickel-based
battery is damaged by excess heat or is marred by uncontrolled
crystalline formation, that part of the battery will not improve.
Other methods, which claim to restore and prolong
rechargeable batteries, have produced disappointing results.
One method is attaching a strong magnet on the side of the
battery; another is exposing the battery to ultrasound vibrations.
No scientific evidence exists that such methods will improve
battery performance, or restore an ailing battery.
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