nc6000 CMOS Battery??

[JimAce]

I have an nc6000 which I got used. The battery is not great but will hold a charge, however after a time of being off, (Overnight) the CMOS memory drops the amount of memory present in the machine.
It causes a warning screen to appear requesting user input to accept the "change" in the amount of memory.It also drops the time and date setttings.
Is there a supplimental battery for the CMOS in the machine? If so I cannot find any reference to it in the Spec sheet.

I hope someone can answer this question. It's becomming a real pain.