NiCd is a strong and silent worker; hard labor poses no problem. It prefers fast charge over slow charge and pulse charge
over DC charge. Improved performance is achieved by interspersing discharge pulses between charge pulses. Commonly referred
to as burp or reverseload charge, this charge method promotes high surface area on the electrodes, resulting
in enhanced performance and increased service life. Reverse load also improves fast-charging because it helps to recombine
the gases generated during charge. The result is a cooler and more effective charge than with conventional DC chargers.
important purpose of reverse load is to minimize the crystalline formation for improved battery performance and prolonged
service life. Research conducted in Germany has shown that reverse load adds 15% to the life of the NiCd battery.
NiCd does not like to be pampered by sitting in chargers for days and being used only occasionally for brief periods. In fact,
the NiCd is the only battery type that performs best if fully discharged periodically. All other chemistries prefer
a shallow discharge. So important is a periodic full discharge that, if omitted, the NiCd gradually loses performance due
to the formation of large crystals on the cell plates, also referred to as memory.
word memory was originally derived from cyclic memory, meaning that a NiCd battery can remember how much discharge
was required on previous discharges. Improvements in battery technology have virtually eliminated this phenomenon. Tests performed
at a Black & Decker lab, for example, showed that the effects of cyclic memory were so small that they could
only be detected with sensitive instruments. After the same battery was discharged for different lengths of time, the cyclic
memory phenomenon could no longer be detected.
problem with the modern NiCd battery is not so much the cyclic memory but the effects of crystalline formation. In
most cases, however, there is a combination of the two phenomenon (from now on when memory is mentioned, crystalline formation
is being referred to). The active materials of a NiCd battery (nickel and cadmium) are present in finely divided crystals.
In a good cell, these crystals remain small, obtaining maximum surface area. When the memory phenomenon occurs, the crystals
grow and drastically reduce the surface area. The result is a voltage depression which leads to a loss of performance. Some
of the capacity may still be present but cannot be retrieved because of the battery’s low voltage table. In advanced
stages, the sharp edges of the crystals grow through the separator, causing high self-discharge or an electrical short.
form of memory that occurs on some cells is the formation of an inter-metallic compound of nickel and cadmium which ties up
some of the needed cadmium and creates extra resistance in the cell. Reconditioning by deep discharge helps to break up this
compound and reverses the capacity loss.
battery’s capacity will gradually deteriorate if repeatedly charged and not fully discharged (never discharge a battery
to 0 volts, 0.9 volts is considered discharged). Another problem with NiCds is a lower cell voltage (1.2 volts) when compared
to single use batteries (1.5 volts). Despite having a lower initial voltage, NiCds provide better performance than single
use batteries due to a much flatter discharge curve. Lastly, the cadmium contained in NiCds is highly toxic and very bad for
the environment. Always recycle old NiCd batteries, never throw them away!
cells should be primed before use. Priming refers to charging then discharging the cell. Generally, a NiCd cell
must by charged/discharged (c/d) 5 to 7 times. In some cases, up to 50 c/d cycles are required before the cell reaches it’s
manufacturers recommend to slow charge a new NiCd battery for 24 hours before use. This initial trickle charge helps to redistribute
the electrolyte to remedy dry spots on the separator that may appear when the electrolyte gravitates to the bottom of the
cell during long storage. A slow charge also helps to bring all the individual cells within a battery pack up to an equal
charge level because each cell may have self-discharged to different capacity levels during storage.
most NiCd batteries are suited for fast charging in an hour or so, fast charge should only be applied between 41°F and 113°F.
When charging a NiCd below 41°F, the efficiency of oxygen recombination is greatly reduced and pressure build up occurs. Sometimes,
hydrogen can be generated as well.
compensate for the slower metabolism at cold temperatures, a low charge must be applied, especially at the beginning and end
of the charge cycle. Special methods are available for charging at cold temperatures. The NiCd is the only commercial battery
that can accept charge at extremely low temperatures.
charge acceptance of a NiCd at higher temperatures is drastically reduced. A battery that provides a capacity of 100% if charged
at a moderate room temperature can only accept 70% if charged at 113° F and 45% if charged at 140° F. This is demonstrated
by the typically poor summer performance.
batteries should be kept in cool and dry storage. Refrigerators as a storage media are recommended, but freezers should be
avoided because not all chemistries are suited for storage in freezing temperatures. When refrigerated, the battery should
be placed in a plastic bag to protect against condensation. Placing a desiccant pouch in the plastic bag is a good
NiCd battery can be stored unattended for up to five years. For best results, a NiCd should be fully charged, then discharged
to 0.9 volts per cell and storage in a cool, dry place. A NiCd that is allowed to self-discharge is subject to formation of
large crystals (memory).
storage of NiCd (and NiMH) requires priming the batteries before use by applying a slow charge followed by one or several
discharge/charge cycles. Depending on the length and temperature of storage, two to five cycles may be required to regain
full performance. The warmer the storage temperature, the more cycles are needed. Some cycling may be required after as little
as two months of storage.