If you're unlucky, you're going to have to replace your motherboard. Real time clock chips are the most reliable of all the battery solutions on PCs today. They look like a black rectangular chip attached to the motherboard and often have a little picture of a clock face printed on them. If you have one, typically you won't have to worry about time-related problems ever again because they last up to 10 years, unless of course they're defective. They can however wear out and corrode.
Some systems use a lithium battery that looks like a small oil drum on the motherboard.
Others are coin-shaped units and are either attached with solder or placed in a holder. Finally, if you don't see a battery like the ones above, you might have a proprietary battery system, she adds. Check with your system's manufacturer or the motherboard manual you received with your system. Even though this port is inside your machine, it's classified that way to differentiate between the internal battery which is also attached to the motherboard. In the event that you do have this feature, you're in luck.