On Tue, 2009-02-17 at 02:32 +0000, Matthew Garrett wrote:
> On Mon, Feb 16, 2009 at 07:02:52PM -0500, brad longo wrote:
> > As I'm sure most of you know, leaving your laptop plugged in and
> > charging with a full battery charge is harmful for the battery. I have
> > been trying to see if Fedora's power management tool has something built
> > in so that when the battery reaches full charge, it will then discharge
> > to lets say around 95% before beginning to charge again. Friends of
> > mine with the same laptop use such measures except they are running
> > windows. However, based on the fact I did not see any documentation
> > about this, and that my battery charge does not appear to fluctuate at
> > all once it becomes fully charged (according to the statistics), I'm
> > guessing no such thing exists in Fedora. Does anyone have any
> > information as to whether this safety feature exists in Fedora, or
> > whether some other measures exist instead? Basically I'm just wondering
> > if I need to periodically unplug my laptop to preserve the lifespan of
> > the battery, which would be annoying. Also if this is not a feature is
> > anyone working on developing something like this for Fedora?
>
> Charging of the battery is generally under firmware rather than software
> control. Laptops will typically stop charging at 100%, at which point
> the battery will slowly self-discharge. When the battery hits some
> threshold (typically somewhere between 95% and 97%) the firmware will
> start charging again.
>
> What you're talking about is presumably an interface to modify that
> threshold. This is device specific. The tp_smapi driver (which is not in
> the kernel for exceedingly dull reasons) allows this to be configured on
> Thinkpads. I don't believe that we know how to on any other systems.
My dual-boot ThinkPad T61 has a Windows power utility that sets the
level at which charging commences. A recent update of that utility
reset the level to 85%. So what happens is that the slow discharge when
suspended or used briefly on battery doesn't result in a recharge until
the level has dropped below 85%. The utility suggests that this
lengthens battery life as compared to, say a 95% or 97% threshold. I
guess the point is mainly to reduce the frequency of discharge/charge
cycles.
--
Matthew Saltzman
Clemson University Math Sciences
mjs AT clemson DOT edu
http://www.math.clemson.edu/~mjs
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