Li - ion batteries and charging question.

[Daneel]

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

 

[PeteS]

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.

Cheers

PeteS

 

[CWatters]

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.

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.

 

[JANA]

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.

--

JANA
_____


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

 

[PeteS]

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) <= Capacity rating (i.e. a 1Ahour cell
would usually be charged in constant current mode at <= 1A)

I(cutoff) usually about I(cc) / 10

Note that on USB, there are strict rules on the amount of current a
device may draw (100mA mostly, 500mA high power), so the charger in
your application won't be doing very much current. Of course, I don't
know what the rating is on the battery you are using, either.

Cheers

PeteS


Cheers

Petes