Desktop CMOS Battery Dies (Useful Tip)

[WalksInSilence]

This may be useful for anyone else using an older than normal Windows PC.

Typically after at least a decade's use (my own experience is actually 12 years) the CMOS battery on a desktop PC's motherboard will start to fail. This is characterized by occasional then more frequent PC boots direct into the BIOS settings. Eventually it will fail completely and reset to the original MB BIOS and the default settings.

The problem you may have is that even after you replace the battery and reflash the BIOS, so you're using exactly the same version, it still may not boot into Windows. In my case it got to the point the Windows 7 icon starts to appear then freezes. If you try the repair options you'll be offered Windows Diagnostic tools will report all OK but one error that can't be identified or fixed.

This is can set you off on a totally unnecessary diagnostic and repair path which will waste your time and probably won't find let alone fix the actual cause.

This is a very minor one BUT if you don't know about it you'll quickly be tempted to go through all those hoops. The cause is that with an older MB the 'optimized' default settings actually return the HDD addressing mode to IDE (Integrated Drive Electronics) when more modern SATA HDDs and SSDs require AHCI (Advanced Host Controller Interface).

All you need to do is go into BIOS, find that setting. See the screenshot below for the location of this setting with older Gigabyte MBs. Swap it back to AHCI, save and reboot. You might get a Windows Diagnostic repair screen option first time but if you just choose to boot Windows normally - with any luck, it will.

Hope this helps someone here avoid the hassle I went through trying to identify the cause of the boot failure after I had to replace the CMOS battery.

       

Edited September 3 by WalksInSilence
typo

[j7n]

Changing BIOS settings is not the same as "reflashing" the BIOS, which shouldn't be needed after changing the battery. Or does it now? Do most drives require AHCI? I've only found this with one drive that was extremely slow in compatibility mode (5 MB/s) because it didn't fully implement Ultra DMA.

[Tripredacus]

Older boards default to IDE/Standard mode for the storage controller, but best practice since at least XP era has been to set that to AHCI before installation. So yes, it is common for a system to not boot when BIOS is reset and this is always the first thing to check. Similarly on modern systems using a supported RAID (JBOD) option if an NVMe is installed instead of AHCI,.

More modern boards from ODMs within the past 2 years have been shipping with a secondary option relating to the storage controller... which name escapes me right now. Basically it is a feature that only has a benefit for RAID but has been found to be enabled by default where AHCI is the default and also on systems that don't even have a RAID option at all... such as notebooks. This feature was annoying at its launch because Windows required a driver to use it (and boot) in addition to the storage driver and Windows versions at the time didn't have a default driver and there wasn't one initially available for WinPE either. I think current Windows 11 has support for this option now but there certainly is an in-between set of Windows builds that have problems. I hate that I can't remember the name of that option but I had primarily seen it on notebooks from Asus and Clevo.