[ltp] X240: Sudden battery death
Henrique de Moraes Holschuh
Mon, 28 Dec 2015 10:41:53 -0200
On Tue, 08 Dec 2015, Jochen Spieker wrote:
> Jeffrey L. Taylor:
> > Quoting Jochen Spieker <firstname.lastname@example.org>:
> >> I usually use the laptop on AC, but every or every other week I need to
> >> unplug it anyway and then try to discharge at least the external battery
> >> completely. Unfortunately, I cannot tell how many charging cycles it had
> >> because cycle_count returns 0 for some reason.
> > Why are you discharging the external battery completely? If it is NiCad
> > (Nickel Cadmium) this is resonable behavior (the memory effect). If it's a
> > lithium battery, this will kill it quickly.
> "Completely" as in "down to 5%, then the internal battery takes over". I
> don't do a deep-discharge, of course.
5% is cutting it too close to deep discharge for Li-ION, especially because
you cannot really trust it to be 5% (and not, say, 3% or less) as the "fuel
gauge" can accumulate a lot of error very quickly.
Keep it above 20% if you can.
> As I said, I am aware that this is not the best way to treat a battery.
> But I am still surprised by it becoming almost useless in less than two
Well, yes, that steep device breakdown curve is quite surprising. If it is
a 3-cell or 6-cell battery, it looks like each cell-group suffered a
breakdown, close together in time...
But if cycle_count returns zero, it might well be battery pack
microcontroller failure (there's one inside the battery pack that is *NEVER*
powered down -- so, it is the one thing that must not have software bugs
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