As far as I know, once they're dead they're dead. Laptop batteriess are actually rated for a rediculously low amount of cycles. (we're talking a couple hundred cycles at most). The problem with sony laptops seem to be that you have to pay outrageous prices for sony branded accesories. A decent dell battery on ebay will cost you $50. A sony one will cost more than doubble that. There are cheaper ones than the BP71, but they don't last as long.

Good luck,
Matthew