An old rig of mine with an Asus motherboard hasn't been saving the fan settings. The motherboard is now getting close to nine years old. It runs Windows 10, but not AI Suite or other Asus software, so fans have to be controlled via the Bios.

This old thing doesn't get used often but works well and can even run 4k gaming. Anyhow, recently, I started it up after not using it for a few months, and the Bios needed to be set up again. I did so, and it worked fine. I imagine the battery needed recharging after that, so left it plugged in for a couple days after updating everything and shutting it down.

Now after starting it up again (the battery ought to be charged fully now) a few times, it has not retained the bios settings. Can anyone explain why this is?

Thanks in advance.