After 6 years, the batteries may well be dead. I've not had one leak yet, and I've just checked my old i486 board.

Few PCs of the last 10 years have batteries soldered in place, and replacement is straightforward. Even if you don't replace the battery, the PC should still work normally. It may not recognise the hard drive, in which case go to the BIOS and tell it to autodetect. It will almost certainly do a Rip Van Winkle impression and insist it's Jan 1, 1989.

The battery powers the CMOS memory, which usually holds only the clock time and the hard disk parameters.

Phil