Hi!
On the Tequatl event my server (Piken Square) reached twice the 75% HP of the boss when I was there, and we defended all of the batteries but even with that I didn’t got the achievement. My guildmates got it (someone just for the second time), but I didn’t. I killed the mobs around the batteries, and I read on the guides that, you just have to defend the batteries to get the achievement, so I think it’s bugged. Please, fix it!