Battery Technology Overview – Part 2
While a nickel metal hydroxide (NiMH) battery has two to three times the capacity as a nickel cadmium battery, compared to lithium ion batteries the NiMH batteries have a lower density by volume and the self discharge rate is higher. An effect called “voltage depression” can occur in NiMH batteries due to partial discharging and recharging; this can lead to premature discarding of the battery but can be reversed if full charge cycling is used. This means a battery is fully discharged and then fully recharged restoring the internal charge memory of the cell. NiMH batteries have been redesigned recently to provide a lower discharge rate and longer life than its previous chemical structure allowed.
The current standard in laptop battery technology is the lithium ion battery; this battery uses lithium ions (Li-ion) to charge and hold chemical energy between the cathode and anode. These batteries are characterized by no memory effect or voltage depression. This means that the life of the battery is not affected by the full discharging of the battery. This alleviates the user from having to remember to fully discharge the battery prior to recharging. Li-ion batteries also exhibit extremely low self discharge rates, about 5% a month as compared to NiMH at 30% total capacity per month at room temperature which is a marked increase in the storage life of a battery. It should be noted that low self discharge NiMH batteries have a 1.25% monthly self discharge rate.
There are a few drawbacks to Li-ion batteries that are not widely known. Lithium ion batteries over time will lose their total capacity simply due to age which is not apparent in other batteries. This happens regardless of use or storage, and is inevitable in lithium ion batteries. High heat levels can drastically reduce the charging and recharging capabilities permanently and this usually happens during an overcharging or when stored in a high temperature area. Even with these few drawbacks Li-ion batteries have one of the highest energy to weight ratios on the market today.
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One Comment on Battery Technology Overview – Part 2
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Σάκης on
Sun, 10th May 2009 1:12 pm
polh kalah h perigrafh kai nomizw oti entopisa to provlima pou exw me thn mpataria mou.enw douleue kanonika,vgazw gia ligo to pc apo thn mpriza,kai to ksanavazw…otan to ekana auto,meta mou elege oti den entopistike mpataria.h mpataria htan plirhs fortismenh.twra einai nekrh…den douleuei.ti mporw na kanw gia na thn ksana epanaferw?
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