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Tuesday, May 12, 2009

Batteries Part 4 Lithium

Lithium cells come in many different sizes and voltages, but by far the most common lithium cell voltage is 3V. Lithium cells can be primary (non-rechargeable) or secondary rechargeable cells. These batteries hold the most power per weight of any in general service. The normal design for these cells is a pack that would take the place of either two or four AA alkaline cells.
Lithium-Ion rechargeable batteries have been taking the place of NiMH packs in digital equipment such as cameras and laptops because their capacity is 2-3 times what a NiMH is. Almost all new laptops utilize a Li-ion battery pack. Night vision gear almost always use lithium batteries, either the primary or the rechargeable kind. These cells exhibit a low self-discharge rate of 5% per month.
Of course, there are disadvantages to go with the advantages. Li-ion cells have high internal resistance, so cannot provide the surges of power that NiCad and even NiMH can. Li-ion batteries also lose capacity dependent more upon time than cycles, so storing these cells away for an emergency will get you nothing. A Li-ion cell will lose 20% of its capacity per year, no matter what. Again, these need a smart charger, and the Li-ion battery packs are known for their propensity to catch fire during charging or even use. 1% of all Li-ion laptop battery packs produced have been recalled for this problem.
For laptops, digital cameras, night vision and other electronics, there is nothing that holds out longer than Li-ion batteries. So far, they are too expensive and finicky for anything else, but there is a lot of skull sweat being expended to fix that.