|
Posted by Ye Electrik Fanne Clubbe on May 12, 2005, 9:09 am
Please log in for more thread options
> I have to disagree with a lot of your post.
>
> While in theory overcharging should not be possible, the overwhelming
> volume of user experience suggests that leaving the battery in the
> laptop will result in loss of life. We can't prove that it's
> overcharging rather than heat, but annectodal evidence suggests
> overcharging, not withstanding the internal microprocessor present in
> most laptop batteries that is supposed to prevent this.
>
> Lithium battery systems are the most chemically stable of all battery
> systems, for both single use and rechargeable. Almost all of the
> battery manufacturers say that they can last 10 years (I posted a bunch
> of references with links several weeks ago in this newsgroup; Duracell
> says "7 years or more", and they are about the most conservative). I
> have box of about a dozen Toshiba PA-2487 batteries here from 1995, 1996
> and 1997 that still run Satellite 400 series laptops for more than 2
> hours each.
>
> Leaving the battery in place when the laptop is primarily and
> consistently run on AC is bad advice whose probable consequence will be
> to "throw away" 50% to 80% of the life of a $200 battery.
>
> About 2 years ago, in this newsgroup, there was an extensive discussion
> of this that went on for thousands and thousands of posts, over about 6
> months. The consensus not of theoretical recommendations and what
> "should" happen but of actual user experience was absolutely
> overwhelming. Take the battery out and use it only when actually
> traveling, it can last the better part of a decade. Leave it in the
> laptop all the time, it will be gone in, typically, 9 to 24 months.
> Even the people who ended up arguing that it was ok to leave it in, in
> the end, ended up being mostly convinced that real world consequence of
> doing so was early destruction of the battery.
>
Part of the issue is that the battery manufacturers won't issue any really
helpful advice on battery life and indeed are quite reticent on the issue.
However, the chemistry is mature enough for the life limiting factors to
have been well established. A lot of misinformation exists on battery life
and limitations. Many things affect the life of batteries and the absence
of any easily found hard and fast information fuels speculation and so
called anecdotal evidence.
When Nickel Metal-Hydride (Ni-MH) batteries first appeared, the marketing
men invented a problem with the traditional Nickel Cadmium (Ni-Cd) to
persuade people to buy the (at that time) more expensive Ni-MH. This
problem is the well known (and non-existent) 'Memory effect'. Ni-Cd
rechargeable technology, is one of the oldest rechargeable technologies
there is dating well into the 19th century. Memory effect was entirely
unknown until the marketing men invented it. You now read and hear about
this everywhere - the effect that people did notice was due to an entirely
different problem that afflicts under-used cells. I have revitalised many a
Ni-Cd battery with 'memory effect' by curing the other problem. The ironic
part is that the Ni-MH technology suffers from a problem that appears
similar to memory effect (but, again, is a different cause - 'voltage
depression').
Lithium Ion batteries are charged using a constant voltage regime for the
last 20% of the charge cycle. The charge terminates when the battery
voltage equals the charger voltage, and the charge current falls to zero (to
be accurate, a very small current equal to its own self discharge - which is
very low for Li-ion). The battery can be left in situ without overcharging.
Just as well as overcharged Li-ions explosively destruct. However, if the
Laptop is badly designed (and many are), the battery absorbs heat from other
circuits, and this will shorten its life considerably and is probably what
started the over charging story that has passed into folklore. Li-ions have
the narrowest temperature tolerance of any chemistry. Allowing the battery
to regularly reach 30 deg C in a laptop - not that unusual (even if
disconnected or otherwise properly looked after) will kill it in under 2
years.
It is true that if you are using the laptop on AC power for lengthy periods
with no intention of using battery power, then it makes sense to remove the
battery regardless.
Depending on how Li-ion batteries are used or abused, can severely affect
their life. I myself have examples here that are 12 years old and still
posses about 70% of the starting capacity. I also have examples that died
in less than a year. My laptop battery is 3 yers old and perfectly
serviceable (though not as much capacity as it used to).
Ian.
| 
XML Sitemap