How does a desktop or laptop computer clock stay synchronized, even after you have turned the machine off for several days, before you switch it back on? Yes, you guessed it right. It's because of the motherboard battery, which keeps the clock ticking all the time even after the desktop or laptop computer is turned off. Besides this function, the battery also powers CMOS memory in some of the old computers. Ergo, when you get a 'CMOS Battery Failure' signal at start up, it's time to get the internal battery replaced.
In this Techspirited article, I present a step-by-step guide on motherboard battery replacement. I only focus on desktop computers which need a battery change. In case of laptop computers, it's best that you let professionals handle the replacement. The reason is not only the complex internal architecture, but also the fact that opening the laptop on your own, voids the warranty. Let us know a bit about motherboard batteries, before we dive into the replacement procedure.
About Motherboard Batteries
Most desktop and laptop batteries are lithium based coin batteries, which are larger versions of the button cells used in wrist watches. They are designed to provide a voltage output of 3 V, to power the CMOS memory and keep the internal computer clock ticking. The standards lithium based coin size batteries are not rechargeable. They typically last for three to more than six years, depending on the usage and motherboard type.
The standard lithium coin cells are known by the code name of 'CR2032'. A new purchase will cost you about $1 to $3 approximately. Since it powers onboard memory modules, a replacement of the battery results into resetting of CMOS and BIOS settings. If you see messages like 'CMOS checksum error', 'CMOS read error' or 'CMOS setting error' on startup and wrong date and time settings, it is most likely that your CMOS battery needs a replacement.
Replacing a Motherboard Battery
Probably the most easily replaceable motherboard part is the CMOS battery. Here is a stepwise guide on how to go about replacing your desktop computer's on board lithium based coin battery.
Step 1: Check Out Battery Specifications & Buy a Replacement
Firstly, you need to find an exact replacement for the existing battery. To do that, you must first check out the exact specifications of the old battery. Switch off the computer, unplug the power cord and open the desktop computer case using screwdrivers. Make sure than you ground the case, wear a grounding strap or use an insulating mat to prevent an electrostatic discharge problem. Locate the battery, which can be distinctly made out by its coin shaped appearance. Note down the model number and brand which is usually engraved on it. Buy a new battery with exactly the same specifications.
Step 2: Note Down CMOS and BIOS Settings
When you remove the battery to get it replaced, the CMOS and BIOS settings automatically reset. So it's essential that you note down both settings, before you remove the battery. That way, you can correctly change the settings later, after replacement.
Step 3: Remove Old Battery
After noting down the settings, shut down the computer and remove power cord. Open the computer casing again and locate the old battery. All the CR2032 are installed horizontally on motherboards with a small tab or knob to hold them in place. All you have to do is push the tab a bit with your finger or screwdriver, to remove the battery. Make sure that you have grounded the case, when removing the battery.
Step 4: Replace With a New CMOS Battery
Now replace the battery with a new one. Put the computer case back in place, connect the power cord and restart the machine. Go into the system settings and change the BIOS and CMOS settings back to what they were before. You will have to set the date and time, back again. With that, your job is essentially done.
Remember to use an ESD wrist trap to prevent an electrostatic discharge from occurring. You should be done with the replacement task in less than five minutes. Make sure that you reset the CMOS setting properly. In case you don't feel confident about handling the job, you can always call in professionals to handle it for you.