why?
could be down to a mains surge
or just a faulty battery
bad news
if you've tried another battery without joy
... it's possible that the surge was passed on to the phone when the battery blew out.
worse news
Batteries are rarelt covered by guarantees ... even quite new ones.
Maybe
it's worth contavting the shop /sony ... there have been lots of cases of faulty Li-Lon batteries recently ....
http://www.infoworld.com/article/03/12/19/50OP reality_1.html
https://www.youtube.com/watch?v=WeWq6rWzChw
you might be lucky and get a replacement