A common difficulty with portable equipment is the gradual decline in battery performance after the first year of service. Although fully charged, the battery eventually regresses to a point where the available energy is less than half of its original capacity (Sony Vaio VGN-FZ battery).

Rechargeable batteries are known to cause more concern, grief and frustration than any other component of a portable device. Given its relatively short life span, the battery is also one of the most expensive and least reliable parts. In many ways, a battery exhibits human-like characteristics: it needs good nutrition, prefers moderate room temperature and with the nickel-based system, requires regular exercise to prevent the phenomenon called 'memory' (Sony VGP-BPS8 battery).

How to restore and prolong nickel-based batteries

When nickel-based batteries are mentioned, the word 'memory' comes to mind. Memory was originally derived from 'cyclic memory', meaning that a Nickel-cadmium (NiCd) battery could remember how much energy was required and would provide similar amounts on subsequent discharges. Improvements in battery technology have virtually eliminated this phenomenon. The modern term of 'memory' is a crystalline formation that robs the battery of its capacity. Applying one or several full discharge cycles can commonly reverse this effect (Sony VGP-BPL9 battery).

The active cadmium material of a NiCd battery is present in finely divided crystals. In a good cell, these crystals remain small, obtaining maximum surface area. Memory causes the crystals to grow, reducing the surface area. In advanced stages, the sharp edges of the crystals may penetrate the separator, initiating high self-discharge or an electrical short.

The effect of crystalline formation is most visible if a NiCd battery is left in the charger for days, or if repeatedly recharged without a periodic full discharge. Since most applications do not use up all energy before recharge, a periodic discharge to 1V/cell (known as exercise) is essential to prevent memory (Sony VGP-BPS9battery).

All NiCd batteries in regular use and on standby mode (sitting in a charger for operational readiness) should be exercised once per month. Between these monthly exercise cycles, no further service is needed and the battery can be used with any desired user pattern without memory concern (Sony VGP-BPL11 battery).

If no exercise is applied to a NiCd for three months or more, the crystals ingrain themselves, making them more difficult to break up. In such a case, exercise may no longer be effective in restoring a battery and reconditioning is required. Recondition is a secondary discharge that slowly removes the remaining battery energy by draining the cells to virtually zero volts. NiCd batteries can tolerate a small amount of cell reversal. During deep discharge, caution must be applied to stay within the allowable current limit to minimize cell reversal (Sony VGP-BPL15 battery).

How to prolong lithium-based batteries

Battery research is focusing heavily on lithium chemistries, so much so that one could presume that all future batteries will be lithium systems. In many ways, the Lithium-ion (Li-ion) is superior to nickel and lead-based chemistries (Sony VGN-FZ460E battery).

A Li-ion battery provides 300 to 500 discharge/charge cycles or two to three years of service from the time of manufacturing. The loss of battery capacity occurs gradually and often without the knowledge of the user. There are no remedies to restore Li-ion batteries when worn out.

Li-ion prefers a partial rather than a full discharge. Avoid depleting the battery fully too frequently. Instead, charge more often or use a larger battery. There is no memory to worry about (Sony VGP-BPS11 battery).

Although lithium-ion is memory-free in terms of performance deterioration, engineers often refer to "digital memory" on batteries with fuel gauges. Repeat small discharges with subsequent charges do not allow the calibration needed to track the chemical battery with the fuel gauge. A deliberate full discharge with recharge every 30 charges, or so, will correct this problem. Letting the battery run down in the equipment to the cut-off point will do this. If not done, the fuel gauge becomes increasingly less accurate (SONY VAIO VGN-FZ4000 Battery).

The aspect of aging is an issue that is often ignored. A time clock starts ticking as soon as the battery leaves the factory. The electrolyte slowly 'eats up' the positive plate, causing the internal resistance to increase. Eventually, the cell resistance reaches a point where the battery can no longer deliver energy, although the battery may still contain charge (Sony VGP-BPS10 battery).

How to restore and prolong lead acid batteries

The sealed lead acid battery, known as valve regulated lead acid (VRLA), is designed with a low over-voltage potential. This is done to prevent water depletion. Consequently, these systems never get fully charged and some sulfation will develop over time.

Finding the ideal charge voltage limit is critical. Any voltage level is a compromise. A high voltage limit produces good battery performance but shortens the service life due to grid corrosion on the positive plate. The corrosion is permanent. A low voltage protects the battery and allows charging under a higher temperature but is subject to sulfation on the negative plate ( Sony VGP-BPS3 battery).

Restoring a sulfated battery is difficult and time consuming. One method that provides reasonably good results is applying a charge on top of a charge. This is done by fully charging a battery, then removing it for a 24 to 48 hour rest period and applying a charge again. This process is repeated several times and the capacity is checked again with a full discharge. The lead acid battery is able to accept some overcharge but too much causes corrosion and loss of electrolyte (Sony VGP-BPS2 battery).

Applying an over-voltage charge of up to 2.50V/cell for one to two hours can also reverse sulfation. During treatment, the battery must be kept cool and careful observation is needed. Prevent venting. Most plastic VRLA batteries vent at 34 kPa (5 psi). Not only do escaping gases deplete the electrolyte, they are highly flammable (Apple A1281 battery).

Sealed lead acid batteries are also available in cylindrical form. The Cyclon by Hawker resembles an oversized D sized cell. If sulfated, applying an elevated charge voltage commonly reactivates the cell. Initially, the cell voltage may rise to 5V, absorbing only a small amount of current. In about two hours, the small charging current converts the large sulfate crystals back into active material. The internal cell resistance decreases and the charge voltage normalizes. When within 2.10V to 2.40V, the cell starts to accept normal charge. If the sulfation is advanced, this remedy does not work and the cell needs replacing (Apple M9848LL/A battery).

When applying over-voltage, current limiting must be applied. Always set the limit to the lowest practical setting on the power supply and observe the battery voltage and temperature during charge. Improving the capacity of an older lead acid battery by cycling is mostly in vain. Such a battery may simply be worn out and cycling wears it further down. The lead acid battery is not affected by memory (Apple A1189 battery).

VRLA batteries are commonly rated at a 20-hour discharge. Even at such a slow rate, a capacity of 100 percent is difficult to obtain. For practical reasons, most battery analyzers use a 5-hour discharge when servicing these batteries. This typically produces 80 to 90% of the rated capacity. VRLA cells are normally overrated and manufacturers are aware of this practice (Apple M8665G/A battery).

Battery Recovery Rate

Restoring batteries 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 (Apple M9677*/A battery).

Not all batteries respond well to exercise and recondition. An older battery may show low and inconsistent capacity readings. Another battery may get worse with each advancing cycle. An analogy can be made to a frail old man for whom exercise is harmful. Such a condition suggests battery replacement (Apple A1148 battery).

Some older NiCd batteries recover to near original capacity when serviced. Caution should be applied when rehiring these old-timers because of possible high self-discharge. If in doubt, measure the self-discharge. A 10 percent self-discharge in the first 24 hours after charging is normal. Discard the battery if the self-discharge approaches 30 percent.

The recovery rate of NiMH is about 40 percent. The lower yield is in part due the reduced cycle life. Some batteries may exhibit irreversible heat damage suffered by incorrect charging. Elevated operating and storage temperatures also contribute to permanent capacity loss (Apple 661-2183 battery).

Lithium-based batteries have a defined age limit. Once the anticipated cycles have been delivered, no method exists to restore them. The main reason for failure is high internal resistance caused by oxidation. Operating the battery at elevated temperatures will momentarily improve the performance. However, the high internal resistance will revert to its former state when the temperature normalizes (Apple M9419ZH/A battery)

Many Li-ion batteries for cell phones are being discarded under the warranty return policy. Dealers have confirmed that 80 to 90 percent of these batteries can be repaired with a battery analyzer. Because no equipment is on hand, the batteries are often sent back to the manufacturers or are discarded without attempting to restore them.

Some Li-ion batteries fall asleep if discharged below 2.5V/cell. The internal safety circuit opens and the charger can no longer service the battery. Advanced battery analyzers feature a boost function to activate the protection circuit enabling a recharge. If the cell voltage has fallen below 1.5V/cell and has remained in that state for a few days, a recharge should be avoided because of safety concerns (Apple M9007LL/A battery).

The recovery rate for lead acid batteries is a low 15 percent. The reasons for the low yield may be due to incorrect charging methods, high cycle count, operating at elevated temperatures and old age (Apple M9008J/A battery) .

The question is often asked whether a restored battery will work as well as a new one. The breakdown of the crystalline formation on NiCd can be considered a full restoration. However, the battery will revert back to its former state if the required maintenance is denied. If the separator is damaged by excess heat or is marred by uncontrolled crystalline formation, that part of the battery will not improve (HP PAVILION DV9700t Battery).

Battery analyzers have become an important tool to test, exercise and restore batteries. The Cadex 7400, for example, accommodates NiCd, NiMH, Li-ion/polymer and lead acid batteries and is programmable to a wide range of voltage and current settings. A quick-test program measures battery state-of-health in three minutes and a boost program reactivates dead batteries. There is even a program to measure the battery self-discharge (HP PAVILION DV2 Battery).

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