Divide “Energy when full” by “Energy (design)”, multiple the result by 100, and you’ll get a percentage. For example, in the screenshot below, we’d do the following math:

(44.8 / 54.3) * 100 = 82.5%

This means the battery currently holds 82.5% of its original capacity. That’s not too bad. You won’t be at 100% unless you just purchased a new laptop. But if it’s low—under 50%, for example—and you aren’t getting much time out of your battery, you may just need to replace the battery.

— OR —

Divide “Energy when full” by “Energy (design)”, multiple the result by 100, and you’ll get a percentage. For example, in the screenshot below, we’d do the following math:

(44.8 / 54.3) * 100 = 82.5%

This means the battery currently holds 82.5% of its original capacity. That’s not too bad. You won’t be at 100% unless you just purchased a new laptop. But if it’s low—under 50%, for example—and you aren’t getting much time out of your battery, you may just need to replace the battery.

Intel’s open-source PowerTOP utility will examine your system and see how well various power-saving features are enabled, even providing some suggestions for how to reduce your system’s power consumption. It’s a command-line tool, so you’ll need to run it from there. You’ll usually find it in your Linux distribution’s software repositories.

For example, to install and run PowerTOP on Ubuntu, you’d open a Terminal window and run the following commands:

sudo apt install powertop

sudo powertop --calibrate

gksu gedit /etc/rc.local

i've just edited the file:

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
/usr/sbin/powertop –auto-tune

exit 0