R51 power issue (solved for now)

[BuddyBoy]

Had a very odd problem with an old R51 that I keep around the house for guests to use.

It had a worn-out battery (27 watt useful capacity) and about 70% charge at the time the problems started. It would not power up, and when I plugged in the A/C adapter, the battery icon would flash amber for an instant, but not light up solid, and the system was unresponsive to the power button. I pulled the A/C power and battery and let it sit, but still nothing would work.

I disassembled it and pulled the CMOS battery, and brought an fully charged battery from work. After I put it back together, now everything works. The battery icon goes on solid when I plug in the A/C adapter, and it boots and runs fine, even with the old battery which is now fully charged (I plan to replace it since the capacity is so degraded). Any ideas what may have caused the problem I was experiencing? I'm wondering if it was pulling the CMOS battery for a while that fixed the problem. I measured 3V across it with no load and put it back in, not sure whether it needs replacing or not.