Packard Bell laptop with Vista + bios

Hi,
I have a Packard Bell laptop with Vista, and the concern is that every night at 3 am battery it lights up, and off until the battery completely empty. In my research I could see that the problem might be related to the BIOS clock, but I do not know how to get vista and if it is really the problem.
If someone could bring me details and help me solve this problem,
I thank you in advance!
