A common difficulty with battery-powered equipment is the progressive deterioration in reliability after the first year of service. This phenomenon is mostly due to premature aging of the battery; a reversible capacity loss that is induced by "memory". This loss occurs gradually without the user knowing. Although fully charged, the battery eventually regresses to a point where it can hold less than half of its original capacity, resulting in unexpected down time.

Down-time almost always occurs at critical moments. Under normal conditions, the battery holds enough power until recharged. During heavy activities and longer than expected duties, a marginal battery cannot provide the extra power needed and the equipment fails.

In many ways, a rechargeable battery exhibits human-like characteristics: it needs good nutrition, it prefers moderate room temperature and, in case of the NiCd battery, requires regular exercise to prevent the phenomenon called "memory"

	Memory
	Regular Exercise
	Self Discharge

Summary

The advancements in battery technology may not be as impressive as those achieved in micro electronics but with today's intelligent battery analyzers, the task of providing quality battery maintenance is simplified and the cost is lowered. By following the maintenance procedures recommended by the battery manufacturer, today's rechargeable batteries are capable of supplying a truly reliable and economical energy source.

Defining Terms

• Cell-mismatch: Cells within a battery pack that have different capacity levels.
• C-rate: Unit by which charge and discharge times are scaled. At 1C the charge current equals the battery rating, that is, a 1000mAh battery is charged and discharged a 1000mA.
• Current-limiting chargers: A charger that keeps the charge current constant during the charge process but allows the voltage to fluctuate.
• Exercise: Commonly understood as one or more discharge cycles to one volt per cell (NiCd & NiMH) with subsequent recharge.
• Memory: Reversible capacity loss found on NiCd and to a lesser extend on NiMH batteries. The modern definition of memory refers to crystalline formation on the cell plates.
• Negative Delta V (NDV): The NDV is a drop in battery voltage after full charge is reached. During the initial charge state the NiCd battery terminal voltage rises quickly, then levels off. After the 70% charge level, the voltage rises again, peaks at full charge and drops slightly.
• Recondition: Secondary discharge which drains the battery of its remaining energy, during which the crystalline formation (memory) is dissolved.
• Self-discharge: Capacity loss due to internal leakage between the positive and negative cell plates.
• Soft cell: A cell whose voltage rises well above the specifications during charging. This high voltage is caused by high cell impedance.
• Trickle charge: Maintenance charge to keep the battery in full-charge state after the charge cycle. Trickle charge compensates for self-discharge.
• Voltage-limiting charger: A charger that limits the voltage after a preset voltage table is reached but allows the current to drop while maintaining the voltage limit.