As mentioned in the thread, short of not being connected to WiFi while being connected to a power source, there are no controls to stop an automatic update download at some point. You can do something like install a tvOS profile which will prevent that (and make sure to delete the already downloaded update).
Can you please instruct me on how may I install this tvOS profile? What should I do exactly?
If this is the only way besides turning wi-fi off I'll do it right now. I have no plans to update iOS, since I want to extract every single minute from my device, I hate the idea of degrading the battery and over time Apple showed to be completely unreliable when it comes to this, given the many iOS 11 complaints and the recent news report about iPhones.
*****
Edit: found a link explaining this process:
http://www.idownloadblog.com/2017/12/11/block-ios-updates/
And a link for the download of such profile:
https://github.com/alexd-p/noota/blob/master/NOOTA.mobileconfig
We need to use Safari for iOS (in the iPAD, or iPhone) and visit the above link. Then click "view raw" in the following page to get the profile.
I tried this + the other steps from the tutorial. It worked! Now my device won't keep pestering me anymore.