How to get info on battery drain rate?

madil86639 · 2021-09-06 14:39:35

I am trying to figure out how to get info on battery drain. I found that /sys/class/power_supply/BAT0/capacity gives battery capacity in percentages, but where can i look for energy losses? I want to get something like n [%/h] info. Also for whatever reason /sys/class/power_supply/BAT0/status gives "unknown" when laptop is plugged and capacity does not go up.
(I am using old x220 lenovo).

mpan · 2021-09-07 00:24:10

Power management and monitoring is handled by UPower (extra/upower). You may communicate with it using D-Bus. EnergyRate is the property you want.

Alternatively, if you want to do that the hard and not very reliable way, you may read whatever is available in “/sys/class/power_supply/$DEVICE/uevent” and either wait for it to be updated automatically (if that works) or trigger udev — by calling udevadm trigger or writing literal string “change” to that file — and either re-read the file or setup a udev rule to react to the CHANGE event.

--- edit
Here is an example, showing accessing the information you asked for. The output is JSON that can be fed to other tools.

#!/usr/bin/env python
# SPDX-License-Identifier: CC0-1.0
# Copyright © 2021 mpan; <https://mpan.pl/>; CC0 1.0 (THIS SCRIPT!)
# Context: <https://bbs.archlinux.org/viewtopic.php?id=269453>
import dbus
from xml.dom.minidom import parseString
import json

bus = dbus.SystemBus()
upower = bus.get_object('org.freedesktop.UPower', '/org/freedesktop/UPower')

devPaths = dbus.Interface(upower, 'org.freedesktop.UPower').EnumerateDevices()
result = {}
for devPath in devPaths:
    dev = bus.get_object('org.freedesktop.UPower', devPath)
    devProps = dbus.Interface(dev, 'org.freedesktop.DBus.Properties') \
          .GetAll('org.freedesktop.UPower.Device')
    if 2 == devProps['Type']:
        result[devProps['NativePath']] = {
            'percentage': devProps['Percentage'],
            'rate': devProps['EnergyRate'],
            'hoursLeft': devProps['TimeToEmpty'] / 3600
        }

print(json.dumps(result))

Requires extra/dbus-python and extra/upower.

Last edited by mpan (2021-09-07 14:14:37)

madil86639 · 2021-09-09 10:27:40

Thank you for answering. Well neigher /sys/class/power_supply/BAT0/uevent nor /sys/class/power_supply/AC/uevent give me the info on power drain (current energy losses). Upower seems to have answer, but another issue is that 'cat /sys/class/power_supply/BAT0/uevent' says POWER_SUPPLY_CAPACITY=98, even though laptop remained plugged all night. Is it because the battery is old? I doubt that upower solves it (it just parse those files isn't it?).

madil86639 · 2021-09-09 11:03:45

The output of upower -d:

Device: /org/freedesktop/UPower/devices/line_power_AC
  native-path:          AC
  power supply:         yes
  updated:              Thu 09 Sep 2021 01:36:24 PM MSK (297 seconds ago)
  has history:          no
  has statistics:       no
  line-power
    warning-level:       none
    online:              yes
    icon-name:          'ac-adapter-symbolic'

Device: /org/freedesktop/UPower/devices/battery_BAT0
  native-path:          BAT0
  vendor:               LGC
  model:                45N1025
  serial:               19839
  power supply:         yes
  updated:              Thu 09 Sep 2021 01:40:25 PM MSK (56 seconds ago)
  has history:          yes
  has statistics:       yes
  battery
    present:             yes
    rechargeable:        yes
    state:               fully-charged
    warning-level:       none
    energy:              36.2637 Wh
    energy-empty:        0 Wh
    energy-full:         36.9186 Wh
    energy-full-design:  62.16 Wh
    energy-rate:         0 W
    voltage:             12.532 V
    percentage:          98%
    capacity:            59.3929%
    technology:          lithium-ion
    icon-name:          'battery-full-charged-symbolic'

Device: /org/freedesktop/UPower/devices/DisplayDevice
  power supply:         yes
  updated:              Thu 09 Sep 2021 01:36:24 PM MSK (297 seconds ago)
  has history:          no
  has statistics:       no
  battery
    present:             yes
    state:               fully-charged
    warning-level:       none
    energy:              36.2637 Wh
    energy-full:         36.9186 Wh
    energy-rate:         0 W
    percentage:          98%
    icon-name:          'battery-full-charged-symbolic'

Daemon:
  daemon-version:  0.99.13
  on-battery:      no
  lid-is-closed:   no
  lid-is-present:  yes
  critical-action: HybridSleep

So it says 98% and it worries me. Also why not just use this output why is it more 'reliable way' to use extra/dbus-python ? Energy rate is 0 because the laptop is plugged and it does not drain power from battery. But it would be nice to know the energy losses for the whole machine (even when it is plugged)

seth · 2021-09-09 12:31:09

The number that should worry you is

    capacity:            59.3929%

Well neither /sys/class/power_supply/BAT0/uevent nor /sys/class/power_supply/AC/uevent give me the info on power drain (current energy losses).

You want to poll /sys/class/power_supply/BAT0/uevent and inspect the difference of POWER_SUPPLY_CHARGE_NOW per time or use POWER_SUPPLY_CURRENT_NOW as a metric.

madil86639 · 2021-09-09 15:23:50

seth wrote:

The number that should worry you is
    capacity:            59.3929%

Can you explain? I thought /sys/class/power_supply/BAT0/capacity gives the capacity in percentage. And it says 98 (used to be 100 but when i unplugged for a minute of so it went to 98). According to https://upower.freedesktop.org/docs/Dev … e:Capacity it means that battery is 40% dead (which does not worry me because I have a replacement )

Last edited by madil86639 (2021-09-09 15:45:32)

seth · 2021-09-09 15:30:03

    energy-full:         36.9186 Wh
    energy-full-design:  62.16 Wh

When the battery left the fab is was built to hold ~62Wh
Now it can only hold ~37Wh (60%) so it has lost more than a third of its original capacity since then to age.

madil86639 · 2021-09-09 15:53:35

Thank you for explaining this. But why is it

mpan wrote:

not very reliable way

to read files from /sys/class/power_supply/ ? And is there a way to get actual energy losses even when laptop is plugged in? Because "EnergyRate" in upower gives the amount of energy being drained from the battery, but what I want to know (if that is possible using laptop alone) is the amount of energy being drained by the laptop right now.

seth · 2021-09-09 16:01:52

I assume he's talking about blindly assuming the device to be available in that position.

powertop will tell you about the energy demand of individual hardware components (but that's not a good way if you want to know what's being drained from the battery)

Trilby · 2021-09-09 16:35:56

I'm not sure why this hasn't been mentioned - but you can just watch the /sys/class/<whatever>/energy_now "file" in a loop.

EDIT: oops, nevermind - I missed that you want a measure of the energy used while plugged in. Frankly I'd just invest a couple dollars on a power monitor you'd put on the outlet. But this is very different from the question in the title - the battery will not be draining at all when plugged in.

Last edited by Trilby (2021-09-09 16:38:57)

madil86639 · 2021-09-09 20:37:12

    energy:              36.2637 Wh
    energy-empty:        0 Wh
    energy-full:         36.9186 Wh
    energy-full-design:  62.16 Wh
    energy-rate:         0 W
    voltage:             12.532 V
    percentage:          98%

Another issue with the upower -d output is that it says energy is slitly smaller than energy-full with laptop being plugged. Is it possible that battery capacity reduced over this period and it does not recalculate energy-full yet? How can I obtain the actual energy-full.

mpan · 2021-09-10 09:27:48

How precise measurement are you expecting? The difference between values is already under 2%, which is a very good result.

madil86639 · 2021-09-10 10:23:44

Yes but over the time actual energy capacity (what is now 36.2637, because laptop is plugged) will decrese even further. How can I recalculate "energy-full" that gives upower(it shows 36.9186)? Or will it happen automatically when the difference become bigger?

mpan · 2021-09-13 03:05:44

You have all the values reported.

Arch Linux

#1 2021-09-06 14:39:35

How to get info on battery drain rate?

#2 2021-09-07 00:24:10

Re: How to get info on battery drain rate?

#3 2021-09-09 10:27:40

Re: How to get info on battery drain rate?

#4 2021-09-09 11:03:45

Re: How to get info on battery drain rate?

#5 2021-09-09 12:31:09

Re: How to get info on battery drain rate?

#6 2021-09-09 15:23:50

Re: How to get info on battery drain rate?

#7 2021-09-09 15:30:03

Re: How to get info on battery drain rate?

#8 2021-09-09 15:53:35

Re: How to get info on battery drain rate?

#9 2021-09-09 16:01:52

Re: How to get info on battery drain rate?

#10 2021-09-09 16:35:56

Re: How to get info on battery drain rate?

#11 2021-09-09 20:37:12

Re: How to get info on battery drain rate?

#12 2021-09-10 09:27:48

Re: How to get info on battery drain rate?

#13 2021-09-10 10:23:44

Re: How to get info on battery drain rate?

#14 2021-09-13 03:05:44

Re: How to get info on battery drain rate?

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