Modern Linux systems generally have low-level power-saving features configured in a smart way for laptops, so the below tools aren't as necessary as they once were.
PowerTOP is a utility created by Intel for diagnosing problems with power consumption. It can scan your Linux system, identify what's using too much power, and provide recommendations. If you're trying to squeeze as much juice as possible from your battery, this can help.
You should find PowerTOP in your Linux distribution's package repositories, so install it like you would any other package. You'll need to run it from a terminal window. For example, on Ubuntu, open a terminal window and run the "sudo powertop --calibrate" command for the most accurate readings and recommendations.
TLP isn't something most Linux laptop users will want to use, but it will often provide a way to wring a bit more battery life out of a Linux laptop. This command-line utility is designed to help you configure much more aggressive power-saving options.
Install it and it will automatically start at boot, configuring your laptop to use a more aggressive set of power-saving options. In other words, just installing TLP and starting it or rebooting should be enough to improve your battery life somewhat. You can also tweak these options yourself. Some users report another half hour of battery life after installing TLP--your mileage will probably vary.
Ultimately, what you do with your laptop affects its battery life a lot, too. If you're using a heavy desktop environment and you have a lot of browser tabs open, you might get better battery life if you used more lightweight software. Sure, that much advice is obvious, but you may be better off switching to a lightweight Linux distribution like Lubuntu that comes with a lighter weight desktop and lightweight software. It's worth a shot if you just aren't getting enough battery life out of your laptop.
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