How can you not find it? For most boards I have ever worked on it is in the lower right hand corner. I just remembered that some boards have the battery in sideway, your board may or may not be like that. ALL motherboards have a battery, it IS there, you just gotta find it. Like I said, it's about the size of a quarter.
Got a digital camera? Take a picture of it, post it, and I will tell you where the battery is.
Can you even get to your bios? If you can, just go to 'Load Defaults'