Why is Ubuntu 18.04 battery life superior to Lubuntu 18.04 in a Dell 7577

Question

I'm struggling with the battery life of this laptop while running Lubuntu. In Windows 10 I'm able to get up to 9.5 hours of life in power save mode. But in Lubuntu 100% charge lasts about 2.5 hours.

The laptop specs are:

• Nvidia GTX 1060 Max-Q
• Intel i7 7700hq (8 threads)

(Yeah I know, I'm using Lubuntu in this machine, I just like Lubuntu very much)

I have display brightness at absolute minimum, tlp installed, powertop auto-tuned. When running prime-select query it returns intel so I'm supposedly using only the intel GPU. I even tried decreasing the maximum speed of the processor to 800Mhz with cpufreq frequency-set -u 800mhz. With all this settings the laptop lives at maximum something like 3 hours, but not more than that. Powertop reporst a discharge rate between 17W and 22W

However, when running plain Ubuntu 18.04 with gnome, in a live USB, with nothing installed, it drains so less battery, I get around 5 to 7 hours of estimated life, powertop reports a discharge rate of 11W or less.

I don't install Ubuntu simply because I really dislike Gnome take on UX (nautilus type-ahead removal, no shutdown without prompt option, etc), and I already have Lubuntu set up with all my necessities.

I tried another distros (Mint, Elementary, KDE Neon, Budgie) in Live USB but none of them consumed so little battery as Ubuntu did, they were around 10W and 15W. My theory is that since Dell supports Ubuntu in many of their laptops (this one at least you can get it with Ubuntu), they made some fine tunning with Canonical, that didn't go directly to Ubuntu derivatives like Lubuntu.

Also I have to note that powertop reports are really weird, saying that Display Backlight consumes up to 18W at times even though the display is at minimimum brightness, I think the nvidia drivers could be a possible cause (maybe the two gpus are working simultaneusly somehow?). Also it reports that the ethernet port is draining 1W o 2W when I'm using only wifi.

In the hardware side of things, I'm pretty sure my laptop is taking a lot of heat even when it is doing nothing (like 50°C), and I'm seeing the "fully charged" capacity of my battery going down in these days to 87% in less than two months.

Here is a powertop overview screenshot.

Lubuntu Powertop Overview (tlp, powertop autotuned, nvidia propietary driver, using intel gpu)

EDIT: Immediatly after posting I rebooted the pc into the Live CD to take the next screenshot, this is right after the previous screenshot with almost the same amount of battery

Ubuntu Live CD Powertop Overview (powertop settings on good only)

Answer 1

Have you installed Lubuntu to the disk? If so, it could possibly the power draw of the HDD. A modern SSD, provided it has lower power consumption, may help. More simply power management is done by xfce power manager - have you tried tweaking there?

The most likely cause, as you've already identified though is your Nvidia driver. I don't have an Nvidia card so I can't help with that. Last time I had graphics driver issues in Lubuntu 16.04 I had to tweak settings in /usr/share '/X11/xorg.conf.d/'.

Hope you get it sorted as I'm a fan of Lubuntu too despite having a relatively powerful laptop. I also want to squeeze as many minutes out of it as possible!

Good luck!

Answer 2

Just to wrap up this question, I've been using lubuntu 18.04 for more than a year now, the problem were indeed the nvidia drivers but fortunately last drivers that are available through package manager have been working great, you can disable the card, however you need to log out and in again, or maybe reboot for it to apply.

I made this script to see battery usage in realtime: https://gist.github.com/mateosss/8ae97cca9be0e731b8aa2f84d8432533

It worked way better than powertop for my needs, there you can get your own conclusions about in which moments the battery drains quicker.

Pro tip: Updating the screen and rendering windows that are updating themselves like videos are a battery drainer, if you minimize them or have them in another desktop, they will not be processed by lubuntu, in lxde at least, I've yet to migrate to lxqt. My consumption in idle is about 4W to 5W, 3W with the screen locked, a great improvement from 20W. Unfortunately my battery paid the consequences of intense use and degraded in these two years to about 45% of its original capacity.