Old Core2 Duo (or just Core Duo?) laptop, Acer Travelmate 4230 with a fresh Linux Mint Cinnamon install. Time on the desktop keeps changing, and it seems to be having issues when it resumes from hibernation, sitting locked for periods of time, sometimes leading to me forcing shutdown by holding the power button down and then rebooting. I'm inclined now t think this is not due to the OS but to a failed motherboard battery. The laptop's main battery is still useful, even though I always have it on the psu.

Do the slow resume and lockup sound like what could be expected from an expired bios battery?

Not expecting an answer from Gilles -- I doubt you've kept using a laptop that old.