HP 48SX invalid data message

[bsala]

Hi, my trusty and much loved HP 48SX hadn't been used for a while, and now the 128K card (#82215A) has a problem. The battery has died, so I guess the data has been corrupted and on switch on, the calculator says 'Invalid card data'. I don't know if this is recoverable, and I suspect my data is long gone, but can the card be resurrected? I tried PINIT, but that isn't valid on the 48SX it seems. Any advice would be welcome - note to self - use it more often, it's great.