I wonder if the main battery is the problem. It is now 4 years old and I think loses its charge very rapidly once it's below 50%.
That's undoubtedly the problem. A good main battery retains a very small percentage of its charge even after it runs down far enough for the Powerbook to put itself to sleep. The tiny amount of power remaining in the main battery is sufficient to retain PRAM settings for quite some time before the backup battery, sometimes called the PRAM battery, has to come into play. An old, weary main battery often doesn't do that: instead, it drains completely, and the backup battery must immediately take over the preservation of PRAM contents, which include the date and time. But it can only hold them for a relatively short time, and if AC power isn't reconnected before the backup battery too has been drained, the contents of PRAM are lost. Like the main battery, the backup battery is rechargeable, but apparently the main battery gets priority over it when both batteries need charging. This is why removing the main battery allows the backup battery to recharge faster.
Replace your main battery, and I bet your problems will be resolved. Caution: if you shop online for a battery, beware of the $40-60 batteries that are routinely offered on Ebay. They are very likely to be Chinese counterfeit junk.
Message was edited by: eww