CELLULAR BATTERIES |
NiCd (Nickel Cadmium)
NiCd batteries are the most economically priced batteries , their charging technique is simple & can be charged faster than other battery types .They also have the higher number of charging /discharging cycles (cycle life) which can approach 1500 cycles, based on battery receiving regular maintenance otherwise the bat cycle life will be reduced by a factor of 3 .in addition, they are able to deliver higher load current than NiMH batteries & are easy to recharge after prolonged storage. improved performance is achieved by interspersing discharge pulses between charge pulses.This charge method is known as reverse load method &it promotes high surface area on the electrodes ,resulting in enhanced performance & service life.& also improves fast charging because it helps to recombine the gases generated during charge. The NiCd are not likely to sit in chargers for days & being used only occasionally for brief period. In fact NiCd bat. is the only battery type that performs best if fully discharged periodically & if omitted the bat.gradually loose performance due to the formation of large crystals on the cell plates, also referred to as memory effect.NiMH (Nickel Metal Hydride)
NiMH are the most common batteries used with GSM phones .Some of their advantages are:
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30 % more capacity over NiCd
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Less prone to memory effect than NiCd. Periodic conditioning need to be done less often
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Fewer toxic metals (environmentally friendly).
The NiMH also exhibits some negative attributes, life cycles is only 500 .Shallow rather than deep discharge cycles are preferred .The bat. long life relates directly to the depth of discharge. Also, NiMH dissipates more heat during charge than NiCd, so it requires more complex algorithm For full charge detection. In addition,it cannot accept fast charging ,charging speed is typically half of NiCd batteries ,thus,trickle charging must be controlled more carefully .
Another disadvantage is that NiMH experiences high self discharge.Its figure is one and half higher than that of NiCd.The NiCd loses about 10% of its capacity within the first 24 hours , after which the self-discharge settles to about 10% per month .
Li-ion (Lithium ion)
Lithium is the lightest of all metals,has the greatest electrochemical potential & capable of providing both high voltage & excellent capacity. Due to safety measures the cellular batteries uses lithium ion instead of lithium metal.
The capacity of the Li-ion battery is at least twice that of NiCd & it has a relatively low self discharge. For safety & longevity reasons,each battery pack must be equipped with control circuit to limit the peak voltage of each cell inside the pack during charge & prevent the cell voltage from dropping too low on discharge in addition to temperature control .With these precautions the possibility of metallic plating occurring due to overcharge is virtually eliminated. Anyway, precaution measures must be taken by the phone user himself ,he must not try to short circuit,overcharge,crush,apply reverse polarity,expose to high temperature ,which may lead to deterioration of battery or physical injury.
Li-ion batteries are the most expensive batteries ,their high capacity & lightweight are the main reasons for manufacturers to still working on improvement to achieve higher capacity,additional safety & lower composition cost material .
Li-ion batteries are expected to power most cellular phones by the year 2000.
