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Crystalline formation is most prominent
if the battery is left in the charger for days, or if repeatedly
recharged without a periodic full discharge. It is not necessary
to discharge a NiCd before each charge. A full discharge to
one volt per cell once a month is sufficient to keep the crystal
formation under control. Such a discharge/charge cycle is
referred to as exercise.
If no exercise is applied for several
months, the crystals ingrain themselves, making them more
difficult to dissolve. In such a case, exercise is no longer
effective in restoring a battery and recondition is
required. Recondition is a slow, deep discharge that drains
the cell to a voltage threshold below one volt per cell. Lab
tests have shown that a NiCd cell should be discharged to
at least 0.6 volts to effectively dissolve the more resistant
crystalline build-up. When applying recondition, the current
must be carefully controlled to prevent cell-reversal.
In respect to restoring weak batteries
through exercise and recondition, not all batteries respond
equally well; an older battery may show low and inconsistent
capacity readings, or even get worse with each cycle applied.
If this occurs, the battery should be replaced. This type
of battery can be compared to a very old man to whom exercise
is harmful. There are older NiCd batteries, however, that
recover to near original capacity when serviced. Caution should
be applied when "re-hiring" these old-timers because
they may exhibit high self-discharge.
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