ED#98 : What Happens When The CMOS Battery Fails?

Ever wondered what happens if your CMOS battery fails? Most of us know that the CMOS settings are retained whenever the PC is powered, but what happens when you turn off the PC? Will those CMOS settings just go poof? Or will they remain intact as long as the power supply remains turned on? Believe it or not, no one knew for sure, so iModAMD decided to test a few motherboards and find out.

The Results

Conclusion

Naturally, the CMOS data would be lost if the CMOS battery is dead / missing / malfunctioning and the power supply is turned off. However, things are not quite so clear-cut when the PC is merely powered off, with the PSU still active.

In four of the six motherboards that iModAMD tested, the CMOS data remained intact as long as the power supply unit was drawing power and of course, connected to the motherboard. That means the CMOS battery was only used to maintain the CMOS settings when there was a complete loss of power to the motherboard.

The MSI and the IBM motherboards, however, were wired differently. Even though the PSU was still supplying power to the motherboard, they relied entirely on the CMOS battery to maintain the CMOS settings the moment the PC was powered off. If the battery was dead or missing, the CMOS data would be lost the moment the PC powered down.

Questions & Comments

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