Judging by the hologram, I've come to the conclusion that the packaging is real but the battery is fake. You can easily open the packaging without damaging it, and it seems that someone has swapped out a real for a fake battery. Possibly a previous customer of this same seller, who subsequently returned the item.
Nice little scam, that. Buy £10 knockoffs from ebay, swap them for real ones from Amazon and return the knockoffs to Amazon.