alt Hacker NewsSurely not for _most_ people, but for people on Hacker News, in the correct age range to have a house, putting 100e aside really does not seem out of whack.
Maybe the author is privileged and it's fine, it's not because you personally can't afford any gift that the author is disconnected, he might not just be talking to everyone on earth.
I think the people that can easily put aside €100 for the birthdays of a dozen or more friends could also just pay the €1600 and buy the battery for themselves outright without having to wait for a birthday "surprise"