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After service, the restored batteries were returned
to full use. When examined after six months of field use,
no noticeable degradation in the restored performance was
visible. The regained capacity was permanent with no evidence
of falling back to the previous state. Obviously, the batteries
would need to be serviced on a regular basis to maintain the
performance.
Applying the recondition cycle on a new battery
(top line on chart) resulted in a slight capacity increase.
This capacity gain is not fully understood, other than to
assume that the battery improved by additional formatting.
Another explanation is the presence of early memory. Since
new batteries are stored with some charge, the self-discharge
that occurs during storage contributes to a certain amount
of crystalline formation. Exercising and reconditioning reverse
this effect. This is why the manufacturers recommend storing
rechargeable batteries at about 40 percent charge.
The importance of exercising and reconditioning
NiCd batteries is emphasized further by a study carried out
by GTE Government Systems in Virginia, USA, for the US Navy.
To determine the percentage of batteries needing replacement
within the first year of use, one group of batteries received
charge only, another group was exercised and a third group
received recondition. The batteries studied were used for
two-way radios on the aircraft carriers USS Eisenhower with
1500 batteries and USS George Washington with 600 batteries,
and the destroyer USS Ponce with 500 batteries.
With charge only (charge-and-use), the annual percentage
of battery failure on the USS Eisenhower was 45 percent
(see Figure 10-4). When applying exercise, the
failure rate was reduced to 15 percent. By far the best
results were achieved with recondition. The failure rate dropped
to 5 percent. Identical results were attained from the
USS George Washington and the USS Ponce.
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| Maintenance
Method |
Annual Percentage
of Batteries
Requiring Replacement |
|
|
| Charge only (charge-and-use) |
45% |
| Exercise
only (discharge to 1V/cell) |
15% |
| Reconditioning (secondary
deep discharge) |
5% |
|
|
Figure 10-4: Replacement rates of NiCd
batteries.
The annual percentage of NiCd
batteries requiring replacement when used without any maintenance
decreases with exercise and recondition. These statistics
were drawn from batteries used by the US Navy on the USS Eisenhower,
USS George Washington and USS Ponce.
The GTE Government System report concluded that
a battery analyzer featuring exercise and recondition functions
costing $2,500US would pay for itself in less than one month
on battery savings alone. The report did not address the benefits
of increased system reliability, an issue that is of equal
if not greater importance, especially when the safety of human
lives is at stake.
Another study involving NiCd batteries for defense
applications was performed by the Dutch Army. This involved
battery packs that had been in service for 2 to 3
years during the Balkan War. The Dutch Army was aware that
the batteries were used under the worst possible conditions.
Rather than a good daily workout, the packs were used for
patrol duties lasting 2 to 3 hours per day. The
rest of the time the batteries remained in the chargers for
operational readiness.
After the war, the batteries were sent to the
Dutch Military Headquarters and were tested with Cadex 7000
Series battery analyzers. The test technician found that
the capacity of some packs had dropped to as low as 30 percent.
With the recondition function, 90 percent of the batteries
restored themselves to full field use. The Dutch Army set
the target capacity threshold for field acceptability to 80 percent.
This setting is the pass/fail acceptance level for their batteries.
Based on the successful reconditioning results,
the Dutch Army now assigns the battery maintenance duty to
individual battalions. The program calls for a service once
every two months. Under this regime, the Army reports reduced
battery failure and prolonged service life. The performance
of each battery is known at any time and any under-performing
battery is removed before it causes a problem.
NiCd batteries remain the preferred chemistry
for mobile communications, both in civil and defense applications.
The main reason for its continued use is dependable and enduring
service under difficult conditions. Other chemistries have
been tested and found problematic in long-term use.
During the later part of the 1990s, the US Army
switched from mainly non-rechargeable to the NiMH battery.
The choice of chemistry was based on the benefit of higher
energy densities as compared to NiCd. The army soon discovered
that the NiMH did not live up to the expected cycle life.
Their reasoning, however, is that the 100 cycles attained
from a NiMH pack is still more economical than using a non-rechargeable
equivalent. The army’s focus is now on the Li-ion Polymer,
a system that is more predictable than NiMH and requires little
or no maintenance. The aging issue will likely cause some
logistic concerns, especially if long-term storage is required.
Simple Guidelines
Do not leave a nickel-based battery in a charger
for more than a day after full charge is reached.
- Apply a monthly full discharge cycle. Running the battery
down in the equipment may do this also.
- Do not discharge the battery before each recharge. This
would put undue stress on the battery.
- Avoid elevated temperature. A charger should only raise
the battery temperature for a short time at full charge,
and then the battery should cool off.
- Use quality chargers to charge batteries.
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