10.6 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.