Li - ion batteries and charging question.

Hi, I have a HP HX4700 Pocket PC that is powered by a Li-ion battery.

I'd like to know what charging cycle would be best to get the longest life out of the battery. I know that some types of battery suffer from the memory effect but I was told that li-ion batteries do not. Is this true?

And if so does that mean it is ok to charge it even if it is half full or whatever?

The reason I ask is that I am using a USB sync and charge cable, so every time I sync my ppc with my home computer it starts charging the battery. I sync them several times a day so the battery doesn't get a chance to discharge fully.

There is a setting supposedly to switch usb charging on/off on the ppc but even when switched off it charges anyway.Will this shorten the life of the battery or will it be ok?

Thanks very much Daneel

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Li+ batteries do suffer after a large number of charge cycles, so for the longest battery life, you should keep that in mind. Whether one calls it memory effect or not is irrelevant, although it is not the same as the classic memory effect found in nickel-Cadmium cells.

Most of the Li+ batteries I use (with chargers) are rated at >80% capacity after 500 charge cycles. My applications are expected to charge / discharge these batteries (in one product at least) for over

1000 cycles.

You can charge a Li+ battery at any time without affecting it's current ability to hold charge in any real way (apart from the total number of charge cycle limitation). Li+ batteries do not suffer from the 'memory' effect problem common to NiCad.



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I'm not sure that much work has been done on this.

Li-ion cells must not be allowed to discharge below about 2.4V per cell. Likewise continious trickle charging isn't recommended either, however the charger will be designed to ensure neither happens.

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NiCad batteries have a limited number of charge cycles, and will have a life span of about 3 years average. Sometimes you can have a lucky one that will last longer. Usually after about 500 charge cycles, or about 3 years, they will start to degrade in their performance. This is actually the same for all chargeable batteries.

The exception is that the newer technology Lithium batteries do not have the memory problems of the NiCad batteries. This type of battery can be charged at any time without having to be properly discharged. Their life cycle is about the same as the older NiCad types.

The recommended charge rate from the battery manufacture should be the best to use. This is depended on the particular battery design.

If you are using a separately bought chargeable battery, and designing your own charging system, you should consult the battery manufacture for the proper range of charging specifications. This also applies to knowing the maximum safe loading, and discharge rates, when running the devices with the battery.

When you have a commercially manufactured product, they build their charger to match the battery type from the battery manufacture. These products are designed to meet speciations that are from the UL, CSA, and EC standards for safety and performance. Altering these specifications, will put the product outside of the recommended application range, and thus may pose a safety, and or performance issue.

If you have a battery that is not charging, and the charging device is in specification, this means that the battery must be changed. There is no proper way to revive an older battery that has been through its life cycle, or has been damaged.

There are publications about how to so-called, "revive" batteries, but these procedures never work for very long, nor are dependable. When these batteries go defective, it is because their internal chemical composition has gone through its life cycle, and or something in the battery has degraded, or has been damaged.

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On the specifics of Li+ charging:

Although each manufacturer has their own recommendations, Li+ and Li-Polymer chargers usually charge at a constant current (details in a minute) up to 4.2V per cell, then charge at constant voltage until the charge current reaches a cut off threshold.

The usual numbers are I(cc)

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