How to monitor battery capacity

Recently battery in my notebook started to behave erratically. It will charge only to 70-80% of its maximum capacity. I suspect that it is probably slowly dying, so I will have to replace it soon, but at first, I will look at several utilities to monitor battery capacity.


You can quickly get battery status using sysfs filesystem without any additional utilities.

$ ls /sys/class/power_supply/BAT0/
alarm               current_now   model_name     status      uevent
charge_full         cycle_count   power          subsystem   voltage_min_design
charge_full_design  device        present        technology  voltage_now
charge_now          manufacturer  serial_number  type
$ cat /sys/class/power_supply/BAT0/charge_full_design
$ cat /sys/class/power_supply/BAT0/charge_full
$ cat /sys/class/power_supply/BAT0/charge_now
$ cat /sys/class/power_supply/BAT0/status

ACPI utilities

ACPI utilities will provide information in a more user-friendly form.

$ acpi -bi
Battery 0: Charging, 50%, 01:44:12 until charged
Battery 0: design capacity 5856 mAh, last full capacity 4785 mAh = 81%
$ acpitool -B
  Battery #1     : present
    Remaining capacity : unknown, 50.14%, 01:44:20
    Design capacity    : 5856 mA
    Last full capacity : 4785 mA, 81.71% of design capacity
    Capacity loss      : 18.29%
    Present rate       : 1372 mA
    Charging state     : Charging
    Battery type       : Li-ion
    Model number       : Dell
    Serial number      : 2372


Intelligent Battery Monitor uses statistical and adaptive linear methods to provide accurate estimations of the time needed until full recharge.

Install ibam package.

$ sudo apt-get install ibam

To view graphs, you need to install gnuplot-qt (KDE) or gnuplot-x11 package.

$ sudo apt-get install gnuplot-qt

Edit /etc/rc.local file as root and add the following commands.

#!/bin/sh -e

# IBAM for milosz desktop user
watch -n 60 su milosz -c ibam > /dev/null &

exit 0

After the system reboot, statistics will be collected every minute as a milosz user, so replace milosz with your username.

Monitor battery capacity.

$ ibam -ra
Bios percentage:            58 %
Battery percentage:         66 %
Soft low percentage limit:  5 %
Charge percentage:          58 %
Bios time left:              1:28:32
Battery time left:           1:55:47
Adapted battery time left:   1:32:53
Charge time left:            1:24:51
Adapted charge time left:    1:45:46
Total battery time:          2:55:36
Adapted total battery time:  2:20:53
Total charge time:           3:23:28
Adapted total charge time:   4:13:37
Profile logging enabled.
Current file: /home/milosz/.ibam/profile-001-charge

View the battery graph.

$ ibam -r --plot
Charge time left:            2:25:06
Adapted charge time left:    2:23:04



It didn’t work for me because of init_acpi_acadapt() returned NOT_SUPPORTED bug.


You can graph battery capacity (or even all available data) using rrdtool, although it requires a little bit more research.

Install rrdtool package.

$ sudo apt-get install rrdtool

I will use ~milosz/.battery directory to store rrd file and shell scripts.

$ mkdir ~/.battery

Read and take note of the maximum capacity value as it will be used in the next step.

$ cat /sys/class/power_supply/BAT0/charge_full_design

Create rrd file to store battery statistics. The maximum battery charge value is 5856 mAh, so I will use <0,6000> mAh as an acceptable range of values.

Stored values:

  • one per minute for the first day
  • one per three minutes for the first week
  • one per five minutes for the first month.
$ rdtool create ~/.battery/battery_capacity.rrd -s 60 DS:capacity:GAUGE:120:0:6000 \
   RRA:MAX:0.5:1:1440 \
   RRA:MAX:0.5:3:5040 \

Create ~/.battery/ script as it will be used to read and store battery charge value. Modify rrd_file for the same reason as earlier.

# Update battery charge level


charge_now=`cat /sys/class/power_supply/BAT0/charge_now`
charge_now=`expr ${charge_now} / 1000`

rrdtool update ${rrd_file} N:${charge_now}

Set executable bit.

$ chmod +x ~/.battery/

Edit /etc/rc.local file as root and replace milosz with your username. Statistics will be collected every minute as milosz user. Execute command directly or reboot the system.

#!/bin/sh -e

# Update battery charge level rrd file for milosz desktop user
watch -n 60 su milosz /home/milosz/.battery/

exit 0

To create create nice looking graphs create ~/.battery/ script and modify rrd_file and destination variables.

# Create "battery charge level" graphs for 1 day, 1 week and 1 month


for period in "1d" "1w" "1m"
  /usr/bin/rrdtool graph - \
    --imgformat=PNG -N  \
    --start=-${period} \
    --end=-60 \
    --title="Battery capacity - ${period}" \
    --rigid \
    --base=1000 \
    --full-size-mode \
    --height=210 \
    --width=590 \
    --upper-limit=6000 \
    --lower-limit=0 \
    --vertical-label="mAh" \
    --slope-mode \
    --border 0 \
    --color BACK#FFFFFF \
    --color GRID#FFFFFF \
    --color MGRID#FFFFFF \
    DEF:a=${rrd_file}:capacity:MAX \
    HRULE:5856#FF0000:"Maximum battery capacity" \
    CDEF:b=a,UN,PREV,a,IF \
    LINE:b#dddddd \
    LINE:a#000FF0FF:"Battery capacity" > ${destination}battery_charge_level_${period}.png

Set executable bit.

$ chmod +x ~/.battery/

Execute it periodically to regenerate battery graphs (use cron to automate task) and view at the graphs located in ~/.battery directory.