YP-R0 not charging. Battery replacement ?

[mkcheznous]

My partner dropped her yp-ro in the bath!.
It was quickly scooped out and she said switched off.
I left it on top of a raidiator for a couple of days to dry out before attempting to boot it.
When it did boot - it went to the charging battery screen even though it was not connected to a power source. From there I could boot the player into play mode and everything seemed to work BUT when I tried to switch off, it jus went back to "charging". I tried a reset but it did the same on boot up.
I left it on the radiator for another day and then tried to boot it. This time it came up with a message saying it had insufficient battery and was shutting down.
I therefore tried to charge it but though the machine works when connected to a usb power source, as soon as I disconnect it, it says it has no power and needs to shut down.
I have dismantled the machine and note that the battery does not warm up when under charge so I am assuming I need to replace the battery.
Any ideas where to get one / what type it is - there is little information on the battery itself other than the rating.