Disabling automatic display brightness?

Hello sevenforums.
First of all, I know there are a lot of threads not only here but on the internet, and mind you I've seen most of them and tried some of the solutions:
1) I disabled "Automatic Display Brightness" for absolutely all Power Plans in Intel® HD Graphics Control Panel.
2) I disabled "Display Power Saving Technology" in Intel® HD Graphics Control Panel.
3) I disabled "Enable adaptive brightness" for all Power Plans and for both On Battery and Plugged In
4) I tried creating my own Power Plan as suggested on these forums I think, but that didn't work as well.
5) I tried disabling "Adaptive Brightness" from running "services.msc".
6) I tried uninstalling Intel® HD Graphics Driver, and it works even with driver uninstalled.

Nothing worked so far. Additionally, this happens only when I work from the battery on my laptop. When I plug it in, it stops. I remember it happened before, but the option 1) I listed above helped me back then, now it doesn't.
Please help me as not only the brightness is driving me crazy, but the fact that all the solutions seem not to work.

I am using Dell Inspiron 3542.

Did you look at the Dell Software installed on the machine?

Okay, quick update, I tested it today with running Ubuntu from a flash drive. As far as I understand this is a hardware "feature" of the laptop, and I'm not really sure I can disable it, I will try to return it while I still can, since I don't see how I can read something from the screen while running from the battery.
To further prove my theory I did the exact same thing on my other Dell laptop, and the screen didn't change brightness, so it can't be battery settings kicking in on Ubuntu.
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It's sad really since I really like the laptop, and the battery holds for around 4 hours. Sorry guys, not a Win 7 problem <3