The battery is usually easy to replace. Open the cases and locate them. Swap them out.
I am using Win98 and WinXP in two PCs which are 6 yrs old and 2 yrs old respectively, but both the PCs seem to encounter the same problem due to CMOS battery.
For the PC that has got win98 installed, the system always reports me the wrong current date as year 1999.
A similar problem seems to appear in another PC with XPSP1 installed.
When I tried to upgrade WinXP-Sp1 to SP2, it also mentioned that the system couldn't install the battery.
I wonder if both PCs have encountered the same problem?