Coin$-$cell batteries are often used to power small devices such as watches and small toys. It's obviously not capable of powering the entire all$-$in$-$one computer. So what is it used for here?

Powers a small amount of RAM so the computer will retain motherboard settings, such as the time and date

Powers a small fan in the computer to keep it from overheating

Powers the optical drive ejection mechanism so a user can remove a DVD even when the computer is shut down

Gives the user a few minutes during a power outage to save her work and shut down the computer