Check laptop battery percentage using terminal

There are 2 methods to do this.

First method

The first method is to use cat to display the content of /sys/class/power_supply/BAT*/capacity 

$ cat /sys/class/power_supply/BAT*/capacity

To see the updated value, refreshed every second. -n1 is for refresh every second, and -d is to highlight any changes.

$ watch -n1 -d 'cat /sys/class/power_supply/BAT*/capacity'

Second method

The second method, is to use upower command. To use this command, you need to know the object paths available for your device

$ upower -e

/org/freedesktop/UPower/devices/line_power_AC

/org/freedesktop/UPower/devices/battery_BAT0

/org/freedesktop/UPower/devices/battery_BAT1

/org/freedesktop/UPower/devices/DisplayDevice

So, to check the my first battery information, use below command

$ upower -i /org/freedesktop/UPower/devices/battery_BAT0 | grep percentage

Same goes with the second battery

$ upower -i /org/freedesktop/UPower/devices/battery_BAT0 | grep percentage