My grand kids were over yesterday and played a bit with the 17" MBP. They didn't turn it off; of course it's set to sleep, but I also have a USB laptop cooler under it. This has happened many times in the past few years with normal operation. Today for some reason when I went to turn it off I noticed it was half on the cooler. When I turned it over to my shock it looks as if the batteries began to self destruct swelling up to extreme. There are three packets inside which have blown up as if they were inflated popping the computer battery case out of the MBP and ripping the metal cover apart. Of course they're replacing it under Apple Care, but I wonder what might have happened without the cooler underneath. They wanted me to mail the battery back to them but I'm reluctant to put anything that got THAT hot into any distribution system. I would guess they're fully discharged now but you can't be sure they're safe. They're going to let me return it to a store; they can decide how to deal with it from then on.