When a computer won’t start, it can be frustrating and alarming. There are many potential reasons for a computer not starting, including hardware or software issues. One possible cause of a computer not starting is a dead CMOS battery.
What is a CMOS Battery?
A CMOS battery, also known as a real-time clock (RTC) battery, is a small battery found on the motherboard of a computer.
It provides power to the CMOS (Complementary Metal-Oxide Semiconductor) chip, which stores important information about the computer’s configuration, such as the date and time, the system’s hardware settings, and the password.
Without a functioning CMOS battery, the computer will not be able to retain this information and will not be able to start properly.
Symptoms of a Dead CMOS Battery
There are several symptoms that may indicate a dead CMOS battery. These include:
- The computer’s clock is resetting to default settings, such as 01/01/2000, every time the computer is turned off and on again.
- The computer is not recognizing certain hardware, such as the hard drive or CD-ROM drive.
- The computer is not starting or is experiencing boot issues.
- The computer is asking for the BIOS password, even though it has never been set.
If you are experiencing any of these symptoms, it is possible that the CMOS battery is dead and needs to be replaced.

How to Replace a Dead CMOS Battery
Replacing a dead CMOS battery is a relatively simple task that can be done by most computer users.
Here are the steps to follow:
- Shut down the computer and unplug it from the power source.
- Locate the CMOS battery on the motherboard. It is typically a small, circular battery that looks like a watch battery.
- Using a small flathead screwdriver, carefully remove the battery from its socket.
- Take the old battery with you to a computer or electronics store to ensure that you purchase the correct replacement battery.
- Install the new battery by carefully inserting it into the socket and making sure it is securely in place.
Reasons To Replace A Bad CMOS Battery
There are several reasons why you may need to replace a bad CMOS battery. These include:
- The computer is experiencing symptoms such as a resetting clock or boot issues, indicating that the battery is dead and needs to be replaced.
- The battery has been in use for several years and is no longer functioning properly. Over time, CMOS batteries can lose their ability to hold a charge and will need to be replaced.
- The computer has been exposed to extreme temperatures, which can damage the battery and cause it to fail.
- The battery has been damaged, for example by being dropped or crushed, and is no longer working.
In general, it is a good idea to replace a bad CMOS battery as soon as possible to avoid potential issues with your computer.
Can You Use Any CMOS Battery Replacement?
It is important to use the correct type of CMOS battery replacement for your computer.
Different types of computers require different types of batteries, so using the wrong type of battery can cause problems.
To find the correct replacement battery for your computer, you can refer to the documentation that came with your computer or visit the manufacturer’s website to find the specifications for your model.
The documentation or website will typically list the type of battery that is compatible with your computer.
Alternatively, you can take the old battery with you to a computer or electronics store and ask the staff to help you find a suitable replacement.
It is important to bring the old battery with you, as the physical size and shape of the battery may vary depending on the type of computer.
In general, it is best to use the correct type of CMOS battery replacement to avoid potential issues with your computer.
Using the wrong type of battery can cause problems such as boot failures or hardware malfunctions.
Final Thoughts
In conclusion, a dead CMOS battery can cause a computer not to start.
If you are experiencing symptoms such as a resetting clock or boot issues, it is possible that the CMOS battery is dead and needs to be replaced. Replacing the battery is a simple task that can be done by most computer users.