ANY battery that has swolen is generally unsafe. It swells when under pressure. If that pressure is relieved by having the casing crack, you're going to ruin your phone and potentially get chemical burns on yourself.
Also, be aware that you cannot just throw the damaged one in the trash, it needs to be recycled or treated as hazardous waste. Procedures for this will vary, contact your municipal services for the correct disposal method.
When things go bad:
http://i.imgur.com/rGoRD.jpg
When things go REALLY bad (a Dell notebook, not a BlackBerry in this case):
http://i.imgur.com/FhqrU.jpg
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![[Image: sharing.png]](http://www.meetcweb.com/files/sharing.png)
