Lots of people saying that Apple only had two options - make old handsets slower, or have them randomly shutdown. Might be a reflection of the culture those commenters are from, but it's disingenuous to assert. Other options existed -- notably to advise the user, as part of the update, via mail-out, etc, that this choice had been made from them, and (optionally) what they could do about it.
What are they gonna do about it, "Yes I do want my phone to shut down immediately instead of continuing to be able use it"?
a) slow the phone down
b) make the battery percentage accurate so that people will know when the battery is empty
I have used Samsung phones for a long time (since Galaxy S4), and I've never had a phone turn off on me when the battery percentage was anything other than 0%. Are we supposed to believe that the maker of the "world's most advanced smartphone" (their words) cannot figure out how to prevent random shutdowns without slowing down the whole phone?