Public bug reported:
I use a laptop as my primary computer, normally left running on AC power
all the time so network connections stay up etc. Under Hardy Heron on a
Thinkpad T61 I just noticed that the battery charging icon was on. It
is normal for laptop batteries to slowly self-discharge and so it's
common for OS's to use ACPI to notice when the level gets below 95% and
then recharge to 100%. That isn't so good for the battery (they last
only N hundred charge cycles even if the amount of charging is very
small) but it's a small effect if it doesn't happen often. However,
from the Gnome power history graph (see attached screenshot) it looks
like when the laptop is in use, charge drops to 95% after only a few
hours, which means that the battery gets topped up several times a day,
an astonishingly high frequency. That has to be pretty bad for its
longevity.
I've observed with my older Thinkpad X40 that the usable battery
capacity went from 105% to around 50% of its design capacity over a few
year period even though the laptop was almost never used on battery
power. I thought this had to do with some combination of high
temperature and manufacturer overstatement of how long these batteries
lasted, but I now wonder if excessive consumption on AC power combined
with overfrequent topping-up is also to blame.
I have heard that the most stressful charge/discharge activity on
batteries is when they are almost fully charged or almost fully
discharged; operation (either charging or discharging) when they are in
the 20%-80% range is very easy on them, and high-cycling devices like
gas-hybrid automobiles carefully keep their battery charge level in the
20-80% range to maximize their lifetime. I've also heard of someone
programming their ACPI hooks to keep their laptop battery charge level
in this range.
One dumb workaround is to simply remove the battery, but that makes the
laptop unbalanced, and the battery is useful as an ad hoc UPS
(uninterruptable power supply) even on AC power. I.e. when using the
laptop on my lap I often knock out the power plug by accident. With the
battery installed I can simply plug the power back in. Without it,
there'd be a poweroff, reboot, fsck, reconnect all network clients, etc.
Even when using the laptop portably, I typically never run on battery
power for more than a few minutes (boot up to check email or look up a
document). For longer sessions I can usually find an AC outlet.
Anyway there are two problems: 1) battery drain should not be so high
when the AC power is plugged in. In fact I don't understand why it is
not zero. 2) There should bea setting to let the charge level get all
the way down to 20% or so instead of 95%, before automatically charging
it when the machine is already on AC power. 20% is enough for an
impromptu UPS or quick portable session. Of course I should be able to
fully charge the battery by clicking something or by plugging into AC
power when it wasn't already plugged in.
These batteries are quite expensive and so messing them up unnecessarily
should be considered a serious bug. Battery longevity (how long the
battery retains its total capacity before you have to buy another one)
is in some ways more important than runtime (how long you can run on a
single charge).
** Affects: ubuntu
Importance: Undecided
Status: New
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excessive laptop battery discharge and charging on AC
https://bugs.launchpad.net/bugs/247098
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