I pulled my Phantom 2 Vision from the closet after leaving it unused for over a year. The battery was in the craft. I removed the battery and noticed that its gray side walls (long rectangles containing warning text) are slightly puffed out, to the point of extending about a millimeter beyond the white plastic outer body. They're a little springy, too. It's been so long since I saw the battery that I no longer recall if this is its normal condition. I pressed the battery test button and all 4 green LEDs light. Is it safe to use?