PB G4 PRAM battery and memory reading?

I'm having this PB G4 for a few years now, and I love it!
Yet a few months ago, the amount of RAM available began to hesitate between 2 and 1 GB. Sometimes it read 1 GB, sometimes 2 GB. Generally a restart used to bring it back to 2 GB. When only 1 GB was available, System information reported "upper slot: EMPTY". So it's not the lower slot, as it was the well-known issue years ago. I swapped the RAM sticks - same behavior.
As the time passed, bringing it back to 2 GB became more and more difficult. At one point it became utterly impossible. I tried another new pair of 1 GB RAM sticks - to no avail. Tried to start it with only one RAM stick - OK for the lower slot, it didn't start with only one stick in the upper slot.
Since it seems that nothing can help now to bring the upper slot back to reason (now it reads as "empty" whatever I do), and as all this arrived gradually in time, I wonder if an old PRAM battery may cause an improper reading of memory in the upper slot? What do you think?
Any suggestions will be highly appreciated.
Thank you in advance.

Intell said:

An old or failing PRAM battery will not cause such a problem. Some Powerbooks have a known defect where one of the memory slots stops working. Your Powerbook may be one of them.

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Thank you for the reply. Still, all searches I've done as of today showed the "lower slot" as having been the PB G4 *classical* slot memory problem. But my PB may be one of the "upper slot: EMPTY" rare cases, you're right.
Thanks again.