I use ubuntu linux. I usually have 6hrs of battery life. However I'd like to squeeze in more.
I'm afraid to use powertop because I don't know if the tweaks are permanent or last until reboot.
How to make them only temporary?
There is no way to make powertop settings permanent, but auto-tune might be
good enough.
To have it run at boot add to /etc/rc.local (or as in your distribution),
an executable script that will be launched on boot, such as:
#!/bin/sh -e
sudo powertop --auto-tune
exit 0
To verify that it launched, reboot and open powertop, go to the "Tunables" tab,
and check that all the options are set as "Good".
Some points:
Keep powertop running while the laptop is on battery, as it needs to collect information about your battery and laptop.
When running auto-tune, powertop may give some errors although it worked as intended.