Punctured cell, it's dead. Bin it. If it's still under warranty, ask for a refund on the value of the battery, not for a new one. Sony don't actually tell you but you are supposed to extract the battery while you use the mains adaptor, otherwise the battery pack fries. They will argue the toss aggressively, and you will probably get no-where, so the best bet is the dealer you bought it from. It's a known problem on a couple of VAIOs although I no longer know which models.