It's not about being asked for an email.
It's about being lied to.
You wouldn't be OK with the New York Times writing that Putin died of a heart attack when it's not true. Why would you be OK with this kind of deception then?
If I click on your link, I took a leap of faith on you. If I then find out that you lied to me, you made my day worse and innocent bystanders like the next guy who actually did have a free ebook will get take the damage.
He could have truthfully said: Show HN: Ebook here but you'll have to enter an email address. Then I wouldn't have clicked and we wouldn't be having this discussion now. I suspect the link wouldn't have been upvoted enough to appear on the front page either.
Also note that if I use a burner account from some spam catching service, I'm externalising my damage on to them. They might be OK with that but it's still shitty behavior on my part. So I don't use throwaway accounts. It's a moral thing. You don't litter in the park. You leave it cleaner than how you found it.
Maybe it's me but I wasn't shown a free ebook. I was shown a "give me you PII so I can spam you" trap website.
If you ask me to give you my PII then it's not free, is it?
Are you not aware how many "free ebook" spams are being sent around, usually from disreputable SEO people begging you to link them from your site? The fact that you registered your own domain is another deep red flag. Clearly there are ulterior motives here aside from "I want to help the world by putting our a free ebook".
I do care about video playback battery performance.
So much so, in fact, that I bought my current laptop specifically so it would last long when watching videos.
Also note that tablets, smartphones, the Macbook Air and the Surface are sold on their battery stamina, and specifically while watching videos. And how would you measure that? Youtube, of course!
Why would you even post this here? Who do you think this is helping?