I've been searching for it for the past 10hrs or so and I cant find any information on where to buy it, how to replace it, or if it even exists. The powerbook's date/time resets every once in a while so I'm sure its the PRAM...
If you ever leave your computer in sleep for a long time, the battery becomes depleted and when you reconnect, your mac will lose the time and date. (Gets reset to a day in 1969). In any case, if this happens to you often when you leave the computer to sleep without AC power and the battery gets critically low, you'll lose the date and time.
At least that's been my experience with powerbooks in the past.