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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.
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.