How to Tell If a CMOS Battery Is Bad?
In computer parlance, CMOS stands for Complementary Metal Oxide Semiconductor. It is a type of memory commonly used to save the settings of the BIOS (that is, the basic input-output system) in your computer. This type of memory requires a constant source of power, the CMOS battery, in order to retain information stored in it. CMOS batteries usually last at least five years, but it is not uncommon to replace the CMOS battery in a computer's usable lifetime. Recognizing a bad CMOS battery can save you from the headaches associated with CMOS memory loss.
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Instructions
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Look for symptoms of a bad CMOS battery. Common symptoms include the system clock no longer keeping correct time, a CMOS checksum error, a CMOS read error, the loss of BIOS settings, and a CMOS battery failure error. If you are not experiencing any of these problems, then you probably do not have a bad CMOS battery. Otherwise, move on to Step 2.
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2
Leave your computer plugged in for 24 hours and then reboot it. Sometimes, particularly after a computer has been sitting unplugged for many months, you just need to recharge the CMOS battery. If the symptoms go away after this procedure, then your CMOS battery is most likely fine. If not, proceed to Step 3.
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3
Replace the CMOS battery. If you still experience symptoms after completing Step 2, most likely your CMOS battery is bad. Unfortunately, the only way to determine for sure if your CMOS battery is bad is to replace it. While the vast majority of motherboards allow you to replace the CMOS battery, there are some that make it impossible. For these, you may need to replace the motherboard. Please refer to your motherboard documentation for details about CMOS battery replacement. If you still experience symptoms after replacing the CMOS battery, you most likely have a faulty motherboard and your battery is probably fine.
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Tips & Warnings
When replacing your CMOS battery, always remember to properly shut down your computer to avoid damage to the operating system installation. Make sure to take the appropriate precautions to prevent damage from Electro Static Discharge when working inside your computer case.
