The PRAM battery in the 1400 is an absolute mhtoerfkuecr to get out. Pop the battery and look at the underside of the keyboard in the battery compartment. Those two discs are the PRAM battery. Now think about how much fun that is to disassemble.

Fortunately they go bad slowly and it sounds like yours maintains enough of a charge to deflake it. I'd cycle charge it a bit, see how much you can rehabilitate it. If this keeps happening, grit your teeth, get the service manual, and prepare to learn some new words. I've done it and I never want to do it again.