Battery for Polaroid Pogo printer. (Hither Green SE13)

Pogo was a tiny colour printer made in the 1990's that prints from a mobile phone. I still have lots of paper for mine to use up, but the battery doesn't hold it's charge any more so I can't use it as a portable printer, which is the whole point. I can plug the printer into the mains to use it - but would love to use it as a portable again. Or if anybody has instructions for replacing cells in a failed rechargeable battery it might be useful. Thanks