Princess Michelle - If your computer doesn't hold the time properly, the battery probably needs changing. The ones I've changed have been somewhere on the motherboard & are similar to a watch battery, sort of . . . meaning round & flat. Usually the battery lasts years! However, we have a computer that needs a new battery about every 9 mos to a year. It usually starts losing about 12 hours & you just think "oh, I set it wrong last time" - but eventually it gets days or months off & won't hold from one boot to the next.
If you aren't comfortable doing it yourself, most any repair shop should be able to do it while you wait. Just tell them why you're bringing it in when you call.
Deb