For those that have questions about the size of the bit, every article starts with "Tools". The tri-wing is size Y1 as the guide says. 5mm is the length of the screw itself, not the size of the bit.
Just replaced a battery myself. The replacement battery (from an ebay seller) is supposed to be genuine, but was missing the "Warning, do not remove the battery" sticker and the "Do not throw in the trash" sticker, and the main sticker was glossy with air bubbles. Not sure if fake or not. But have been working great this first night.
This guide was spot on. Followed every step, and used the iFixit kit when doing the repair.