cmos battery

[norman]

The other day, when booting up I pressed 'Esc' in order to select a
particular version of the kernel. To be certain I pressed the key
several times and, eventually, got a message telling me that there had
been a cmos battery failure and to press 'enter' to continue. Booting
restarted and I was able to select the kernel I wanted. I now get this
message every time I boot.

Does this message mean anything disastrous, what adverse effects do I
need to look out for and is there any way I can check to see if the
message is valid? Please advise.

Norman