What does it do?

[Zephik]

What does that lil battery in the motherboard do?

[nil8]

It's the battery that runs your CMOS.
They don't run out for many years. When they do, your time will reset over and over again in your bios.

[Zephik]

oh okay... well my friend just pulled mine out for about an hour. I haven't noticed anything wrong yet... so do I have anything to worry about? btw, It's back in now. lol FYI - dont screw with another guys MSN Messenger when your computer is just sitting there to be effed with while you take a shower.. lol

[Bucko]

The only thing that would have happened is your BIOS would have been reset to stock settings, so any changes you may have made in there for boot order or overclocking etc. have been lost.

No harm should have come to your computer though.

[nil8]

Bucko is correct. Your bios will set back to default settings, including any bios password.

[XcOM]

........ including any bios password.

not always true, my system keeps the password if i remove the batt, i left the battery out for a few days and it didn't reset it, sometimes the password is stored in the BIOS rather than the CMOS.

[nil8]

If that's the case then there should be a jumper on your mobo for either bios default or bios password reset.
I haven't come across a single motherboard that doesn't have a way to reset the bios password so you can enter it or boot your machine just in case.