This thread gives details of the cells needed to replace your backup battery. They are common and cheap, I found that the soldering was not especially difficult, and the replacement backup battery that I fabricated worked. The old cells were actually leaking when removed, so it was a good thing to do.

My hunch is that if your machine will start, sleep, etc. with occasional GLOD, the most likely explanation and so the first port of call is that your backup cells are needing replaced.