I have no Unitiserve experience but I have worked on lots of IT gear running XP embedded, often with Phoenix bios.
Your first screen shot shows that the Unitiserve has found the hard drive and it appears to correctly recognise it, the capacity, cylinder, head etc all look good. The second screen shot is interesting. Normally the hard drive is on channel 0 master but yours is on channel 2 master. I suspect that the failing CMOS battery has caused the BIOS to reset to factory defaults and it is now trying to boot from a non existant drive on Channel 0. Somewhere in the BIOS is a boot sequence setting, have you checked that it is set to Channel 2 Master?
Mike