I can't find the battery. I've checked the entire map and it's no where to be found. The only areas I can't access were behind the waterfall and the elevator that needed the battery. I thought maybe if I raise the water in the upper area would stop the waterfall. So I did that, and then sprinted across before it could kill me. So now I'm stuck down there and can't get back to the mansion. Because the battery simply isn't on the map. It's not in the room where you push the bookshelves out of the way.