best thing to do, is to take a note of all the settings in the BIOS as when you remove the battery, they will be lost. Simply re entre then after you have replaced the battey, and everything should be fine.
click here and get this one, it synchronises your puter clock each time you connect and it puts a customisable [skins] clock face on your desktop. It will also chime on the hour.
It is free but for about £7 you can get the full version, I can't remember what else you get apart from 1/4 hour chimes, I just use the free version to keep my clock on time and the hourly chime is a constant reminder that I should be in bed.