Monitor Going Black

My strawberry iMac G3 333mhz just started having monitor problems. I'll open a pdf or a photo in photoshop and for an instant the screen fades to black and then comes up again, as if the act of opening a large visual is draining the power. I remember having to replace a battery in my old powermac 6115. Does the iMac have such a battery and if so, what is it called and how do I get to it? Or do ya'll think it is another problem? Thank you!