I have an older model MBP ( 07 or 08 model ) with a replaced battery about 2-3yrs ago. Sometime last year I noticed a bit of swelling on the underside of the battery and thought it best to remove it and just run my laptop off mains power. I left this battery sitting around for the last 5-7 months ( just sitting on one of my desks ) and when I found it today, my gosh, what a sight. Click to view full size! Click to view full size! Click to view full size! Click to view full size! I had a brief google search for similar issues and read that this had happened before but was later solved in an updated version of the battery pack. Scary thing is that my battery IS the new version.