Memory: Myth or Fact
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 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 ,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 concerning 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 utilized 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.
Summary Each battery system has a few shortcomings: The lithium family ages and has limited load current; the NiMH has a relative shore service life; the lead acid family is bulky and requires long charge times; and the NiCd has memory. But the NiCd makes up by being the most enduring battery. In addition, it has the lowest cost-to-energy-ratio of all commercial rechargeable batteries.
To achieve long life, some simple guidelines must be observed. They are: 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.
Links : digital camera battery  HP laptop batteryÂ