System Battery Voltage Low

When I first power up my pc (a dell dimension 8300) (Win XP Pro) I get the following message:

Alert! System Battery Voltage is Low; press F1 to conitnue; F2 to run set-up utilitly.

Then I hit F1 and everything loads correctly. Do I need to replace some kind of battery? Any ideas? Help

-Guru

 

http://hardware.mcse.ms/archive10-2005-11-257641.html

 

here is the picture