Yeah CMOS battery is one of those things that you always tell people to check as part of the list of things but never assume it is going to actually do anything!
It seems to be a lot more common these days that it actually fixes something. Not sure if that's 'cause they're using cheaparse batteries these day or if there's something about how the bios has to interact with hardware.
Used to be the biggest issue was that it would cause a motherboard to double boot every time because it wouldn't keep the memory profile.
Check the battery with a Greenlee power tedger?
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