Battery Swollen When Not in Use!

My wife lost her BlackBerry so we had the provider send out a replacement SIM which I intended to use in my 9000...
This had been sitting in a drawer uncharged since around Dec 2011
The battery was inflated to a point where it had pushed off the rear cover and broken the catch...
Nice !
Out of interest I checked my 8900 ( In another Drawer )
Same story...
Must be some chemical reaction going on there..
Anyone else seen this ?
WW

I have not seem this in phone batteries, BUT I have in other batteries. It's always a good idea to remove the battery if you are going to let something sit along time. HOWEVER in this case you might be ok, as long as the battery did not leak, the device SHOULD be ok. The battery MUST be replaced!