kern/173414: ACPI battery time incorrect

J B jb.1234abcd at
Tue Nov 6 09:10:01 UTC 2012

The following reply was made to PR kern/173414; it has been noted by GNATS.

From: J B <jb.1234abcd at>
To: bug-followup at, jb.1234abcd at
Subject: Re: kern/173414: ACPI battery time incorrect
Date: Tue, 6 Nov 2012 10:07:47 +0100

 $ sysctl -d hw.acpi.battery.time
 hw.acpi.battery.time: remaining time in minutes
 Why is it impossible or improper to compute and show battery's remaining
 time ? Because the machine is on on-line power supply ?
 The battery's state, that is, its remaining time, is still valid and of
 interest to user at any machine state (load, etc), regardless of power supply
 being on-line or off-line.
 I want to know WHAT IF, at any time (without or with consideration of current
 machine state (load, etc) in the computation of battery remaining time),
 I disconnected the on-line power supply, could I expect to happen to my
 machine with regard to expected length-of-time availability of battery power
 If you think that the battery's "percent capacity remaining" is enough, then
 you are mistaken. percent capacity remaining
 The battery's "percent capacity remaining" is misleading because its max level
 is degrading over time (the 100% of a new battery is not the same 100% after
 a year or so of random discharging and charging). They just do not tell me
 how much estimated run time I would have as I explained above.
 This is what Linux shows about my battery state:
 $ cat /proc/acpi/battery/BAT0/info
 present:                 yes
 design capacity:         56160 mWh
 last full capacity:      38720 mWh
 battery technology:      rechargeable
 design voltage:          10800 mV
 design capacity warning: 1936 mWh
 design capacity low:     200 mWh
 capacity granularity 1:  1 mWh
 capacity granularity 2:  1 mWh
 model number:            COMPATIBLE
 serial number:            2413
 battery type:            LION
 OEM info:                BATSZ
 $ cat /proc/acpi/battery/BAT0/state
 present:                 yes
 capacity state:          ok
 charging state:          charged
 present rate:            0 mW
 remaining capacity:      38720 mWh
 present voltage:         12405 mV
 These are the original and degraded capacity values of 100% I am talking
 design capacity:         56160 mWh
 last full capacity:      38720 mWh
 remaining capacity:      38720 mWh
 So, please compute this
 hw.acpi.battery.time: remaining time in minutes
 and make it available at any time, and at any state of the machine.
 There is a good use for this data.

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