CMOS Battery lasts 6 months

This has been going on for a few years now, I don’t think that the system was this way to begin with, but the CMOS battery fails after about 6 months on a regular basis. This is a NEC Ready GT100, 450mHz, 256K ram, w/Fujitsu 12gb hd & running Win XP Pro, an upgrade from Win 98SE. Could there be a problem with the hardware, MB, or BIOS settings? I really hope to avoid fiddling w/the BIOS, as it is working now, just a pain in the tokas to change battery more often than I change my sox! Well, almost,ha ha.