Date Changing Sporadically

I recently uprgraded from XP to Vista Home Premium.

When I let my husband borrow my laptop sometime and only sometimes the date
is really wrong. I mean like June 07, May 07 etc.

This has never happened when I am using it. Only when I get it back after he
has used it.

I know, its like when the car works for him and not for me. I don't know.

I was told it was a battery issue, but I have the upgraded longer battery
and I really do not think it is a battery issue.

Are other people with Vista getting this issue?

Any suggestions are appreciated.