https://bugzilla.kernel.org/show_bug.cgi?id=41062
Summary: Incorrect battery capacity after power up/reboot on
recent Thinkpads
Product: ACPI
Version: 2.5
Kernel Version: 3.1-rc1
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: Power-Battery
AssignedTo: acpi_power-batt...@kernel-bugs.osdl.org
ReportedBy: kamil.54...@iskra.name
Regression: No
Recent Thinkpads (I'm seeing this on last year's x201 as well as this year's
x220, but not on older T61 or T42) display incorrect battery capacity in
/proc/acpi/battery/*/*.
The bug is easily reproducible, but subtle. These recent Thinkpad models have
a weird "feature" that the battery charge in /proc/acpi/battery/*/* is
initially (after power up/reboot) reported in mAh, but after a suspend/resume
cycle while running on battery, it changes to mWh.
Here's /proc/acpi/battery/BAT0/info after reboot:
present: yes
design capacity: 2886 mAh
last full capacity: 2909 mAh
battery technology: rechargeable
design voltage: 14800 mV
design capacity warning: 145 mAh
design capacity low: 13 mAh
cycle count: 0
capacity granularity 1: 1 mAh
capacity granularity 2: 1 mAh
model number: 42T4899
serial number: 21064
battery type: LION
OEM info: SANYO
After a suspend/resume cycle the output changes to:
present: yes
design capacity: 28860 mWh
last full capacity: 29090 mWh
battery technology: rechargeable
design voltage: 14800 mV
design capacity warning: 1454 mWh
design capacity low: 200 mWh
cycle count: 0
capacity granularity 1: 1 mWh
capacity granularity 2: 1 mWh
model number: 42T4899
serial number: 21064
battery type: LION
OEM info: SANYO
Can you see how the values for "design capacity", etc. differ by a factor of
10, instead of 14.8 (the design voltage of this battery)? On the battery
itself it says: 14.8V, 1.95Ah, 29Wh, so clearly the values reported in mWh are
correct and the ones in mAh (right after power up/reboot) are not.
Common Thinkpad batteries are rated at 10.8V, so the error with them is just 8%
and probably that's why it hasn't been reported so far. However, I got a
smaller 4-cell battery rated at 14.8V, and with this battery there is a huge
discrepancy in powertop between immediate vs long-term power estimates.
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