02-20-07, 10:07 PM
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#4 (permalink)
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Aximsite Hall of Fame
Join Date: Nov 2003
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Location: Fairfax, VA
PDA: Axim X51v
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Li-Ion batteries like the ones in the Axim line start to decay about 2 years after manufacture. Note, that's manufacture, not the date you put it in service. However, the roll off is very slow. To make the battery last as long as possible, avoid deep discharges and keep it topped off as much as you can. Try to keep it above 70% as much as possible.
From the Ultralife battery support page:
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Unlike nickel-cadmium and nickel-metal hydride rechargeable batteries, lithium-ion (li-ion) rechargeable batteries have no memory effect, therefore, it is not necessary to fully discharge your battery before recharging. Actually, li-ion batteries will generally last longer if you do not completely discharge them before recharging. For example, if you regularly recharge a li-ion battery only after discharging it completely (known as "100% Depth of Discharge"), you can generally expect to obtain between 300 and 500 charge-discharge cycles. However, if you recharge the battery after only a partial discharge, e.g., 50%, you can expect to achieve over 500 charge-discharge cycles; even more if you use a lower depth of discharge, such as 20%. Therefore, you can effectively recharge li-ion batteries even if they have only been discharged for a short time.
To maintain a healthy battery, follow the device manufacturer's charging recommendations, and do not expose the battery to temperatures above 60 degrees C (140 degrees F).
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Lithium ion battery life is described by the number of full charge/discharge cycles that the battery sees. In general most manufacturers specify a cycle life ranging from 300 to 500 full charge/discharge cycles. That means fully charging the battery and then fully discharging it before recharging, also described as "100% Depth of Discharge." To increase the total life of a lithium ion battery it is recommended that the battery be recharged after each use or every few uses, rather than waiting for it to become fully discharged. Total battery life can vary depending on the device in which it is used and recharged. Li-ion batteries reach end of life when the battery reaches 80% of its original capacity, which generally occurs between 300 and 500 cycles of use.
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The shelf life of a lithium ion battery is dependent upon its date of manufacture, storage temperature and state of charge during storage and maintenance charge frequency. It is not possible to give a definitive answer to your question, since quality of manufacturing varies widely in the industry. One manufacturer could make a battery who's impedance increases 10% in two years, while another could make a battery who's impedance increases 50% in that same time frame. These differences are a function of manufacturing processes and materials. In general, one is better off buying a battery with a recent date code than one greater than one year old.
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