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Wednesday, November 26, 2003

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Cerebus

The iPod battery is a lithium polymer battery common in modern electronics, particularly laptops. Lithium polymer batteries don't have a memory like nickel cadmium, hold more charge, and are lighter than even lithium ion. There are other advantages, but these are the main ones.

However, lithium polymer batteries have a useful lifetime of about 300 to 500 charge cycles, due to the chemical reactions that take place when the battery heats while charging. This limit is unavoidable at the moment. This is also why chargers for these batteries contain circuits to limit the charge rate as well as cut off charging when it's complete.

At one recharge a day, that's anywhere from 12 to 18 months of life. Partial charges also count, though less, against the battery life. Particularly counter-intuitive is the fact that the battery will discharge slowly while the unit is connected to external power, but the charge circuits will not "top off" the battery until charge levels decrease below a threshold. So even if your unit spends most of its time connected to external power, battery life is still being consumed, though more slowly.

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