Abnormally high battery discharge rate on Lenovo T420

[Luís de Sousa]

I have upgraded from12.04 to 14.04 on a Lenovo T420 laptop (Corei7-2620M CPU @ 2.70GHz × 4 + Sandybridge Mobile). Whereas with 12.04 the battery discharge rate would stay somewhere between 10 - 12 W/h, with 14.04 it remains persistently over 30 W/h.

The discharge rate came closer to normal after an upgrade by late May. But last week, apparently after an upgrade to linux-headers-generic, the abnormally high discharge rate is back.

This thread at AskUbuntu details what I have tried (unsuccessfully) to identify the cause of this problem:

http://askubuntu.com/questions/461620/ubuntu-14-04-draining-laptop-battery-quicker-than-in-12-04-1-hour-versus-4-hou

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-core 1:0.220.2
ProcVersionSignature: Ubuntu 3.13.0-32.57-generic 3.13.11.4
Uname: Linux 3.13.0-32-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.2
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Wed Jul 23 11:15:26 2014
InstallationDate: Installed on 2011-07-22 (1096 days ago)
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Release amd64 (20101007)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
Symptom: release-upgrade
UpgradeStatus: Upgraded to trusty on 2014-05-02 (81 days ago)
VarLogDistupgradeTermlog:

[Brad Figg (brad-figg)]

This change was made by a bot.

[Joseph Salisbury (jsalisbury)]

Would it be possible for you to test the latest upstream kernel? Refer to https://wiki.ubuntu.com/KernelMainlineBuilds . Please test the latest v3.17 kernel[0].

If this bug is fixed in the mainline kernel, please add the following tag 'kernel-fixed-upstream'.

If the mainline kernel does not fix this bug, please add the tag: 'kernel-bug-exists-upstream'.

If you are unable to test the mainline kernel, for example it will not boot, please add the tag: 'kernel-unable-to-test-upstream'.
Once testing of the upstream kernel is complete, please mark this bug as "Confirmed".

Thanks in advance.

[0] http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.17-rc1-utopic/

[Luís de Sousa (luis-de-sousa)]

I managed to install and run the mainline kernel (3.17). With it the battery discharge rate is dramatically down, about half of what it is with kernel 3.13 (~ 15W), but still above what it was with Ubuntu 12.04. Also, with kernel 3.17 it seems the automatic screen dimming is not working.

Cheers.

[Luís de Sousa (luis-de-sousa)]

A Windows user reports a discharge rate of 7-8 W/h running Word, with WiFi and Bluetooth off:

http://forum.notebookreview.com/lenovo/574678-thinkpad-t420s-owners-thread-10-print.html

With kernel 3.17 and no programmes running the discharge rate is about the double of that.

Reagrds.

[Luís de Sousa (luis-de-sousa)]

Presently I have kernel 3.13.0-48-generic installed (from the automatic updates). With Bluetooth and WiFi off I am able to bring the discharge rate down to 12 W/h. Although now I have battery lifetimes in line with those I had with Ubuntu 12.04, there is still a long way to go to catch Windows.