Clock not retaining time

The system clock on my iMac (350Mhz G3 Slotloader) has started forgetting the date and time. It has to be reset every time the machine is turned on, (a nuisance, but easily doable), otherwise it thinks it's 12 am on 1 January 1904.

There was a widespread power outage in our region for about one second on Friday evening, and I'm wondering if that might have affected the clock circuitry somehow, possibly killed a clock battery. Any idea how to get at the thing to check it out, or is it simply a matter of pulling the whole machine apart and looking for a fried component. Everything else seems to be working fine.

Al Preston