Hi Nigel,
I've not had it from new.
Like you, I was amazed to think of a digital piano being designed without a "permanent" memory - hence my initial question. I couldn't believe it when my registrations disappeared every day.
However it seems that it is indeed the case that this model only has a memory of 80mins (not timed mine exactly but I've known it keep the settings for 2 hours).
I have actually been inside it as one of the monitor speakers was vibrating on E4, obviously something like a minute piece of dust as I couldn't see it but a blow with a can of air sorted it. Therefore it will be a simple job to swap the battery, but I don't think it will change anything.
Have you got a Technics piano?
Regards,
Mike.