I don?t get rid of “battery failure”

I have a 14 year old Commodore PC40 III.
Since a few days he always shows me “battery failure” while starting up. I opened the PC and wanted to change the battery, but on the board there isn?t any battery. Instead of them is a label with “Rev. 8.2B” written on it.

Can anyone of you tell me how to fix that problem.
It?s very important cause of financial datas are on the HD of this Commodore.