Troubleshooting CMOS Battery
Have you ever wondered how the time on your computer stays current, even after it has been turned off? A very small chip that is supported power wise by a little flat battery about the size of a dime holds the time information and system settings. The computer’s BIOS (Basic Input/Output System) is firmware that loads system information that is vital to the boot process and is stored on this tiny chip called CMOS. CMOS (complementary metal oxide semiconductor) is a chip which consumes an extremely low amount of power. So when the computer is off it starts feeding off of the small battery that supports it.
So what happens when you boot your computer and it stops you, asking for system configuration or you actually get to the Windows screen and the time is way off or you got other massages like CMOS Read Error, CMOS Battery Failure, CMOS Checksum Error? This typically happens when the CMOS Battery is dead or dying. CMOS batteries typically last around 4-7 years so it isn’t something that most people have to deal with. After this amount of time they usually upgrade to a new motherboard or buy new computer any way.
There are a few things that can cause the battery to malfunction
- If the computer has been completely turned off for an extended period of time (including power cord is off). Typically this would have to be around 12 months or more of being off, which is not likely to affect most of the people.
- Static discharge. This can happen if you do not take the proper precautions when you are working inside the chassis of a computer. While static shock can be an annoying jolt to us, computer components can suffer irreparable damage because of static shock. The CMOS components are incredible sensitive to static shock and the smallest jolt can ruin a chip so the battery “appears” to be not functioning. Remember to always ground yourself to eliminate the threat of static shock.
- Battery life ending prematurely. Sometimes the battery is defective and dies earlier than it is supposed to.
Fixing the CMOS Battery Isue
Now in any process you want to take the proper troubleshooting steps before going all out, like changing the battery. If you are able to get to Windows or BIOS, try to change the system time back to the current time then save and restart. If the time is off again or you are stopped from loading Windows because it is requesting that a time is entered into the BIOS, then you will need to replace the CMOS Battery. Now, if it boots up and the time is correct you need to turn it off completely including disconnecting the power cord, wait for couple of minutes, press power button few times then connect back the power cord and press power button to turn the PC on. If at this point it boots up fine and the time is correct the CMOS battery is fine, otherwise you need to change it. You also can check the voltage of this battery by using voltmeter, it should be around 3 volts or whatever is written on the battery itself.
Can a PC boot up with out a CMOS battery or when the CMOS battery is dead?
Yes, in most cases there is no problem whatsoever if the power cord stays plugged in and the power supply is always switched on. But if you turn it off completely including power cord you will be asked to edit BIOS settings including the time and date.
Okay so now that we know what can cause the problem, let us go about fixing it.
So of course you need to find the battery first. What does it look like? Below are a couple of pictures showing what a CMOS battery actually looks like on a mother board.
The CMOS Battery is located in different places depending on the computer motherboard, but what is consistent is that it usually looks the same if your computer is not that old. Typically it looks just like a coin. Before you go and decide to change the battery, you have to make sure that you take the precautions to protect the computer from static shock that can cause irreparable damage to system component where the CMOS is extremely sensitive to static shock. Using a ESD (Electro Static Discharge) Wrist Strap will make sure that the computer is adequately protected, if you don’t have ESD strap you should at list make sure you touch the PC case on the plain metal part where is no paint. Now that you have the static under control you are ready to replace the battery. Usually in newer PCs there is a release clip that will allow you to pop the battery out.
Obtaining battery information
Before you buy a new battery you should determine the type of battery that you have. Here are few different types of CMOS batteries found in computers:
Your old battery will usually have all information written on it and you will need to write it down or ideally you should take it to a place you are planning to obtain a new one from. If you are unable to read the battery info a sales representative will help you with it.
Replace the battery with a new one and then turn on your PC. Yes it is really that quick. Upon booting the computer for the first time you will have to reset the system date and time in the BIOS. It should prompt you before the operating system loads. After that, Windows will load and the proper time should be reflected.
If for some strange reason the system time is still acting funny, run anty-spyware and antyvirus programs to make sure that you eliminate that from being a reason. Otherwise the battery you just put in may be defective or motherboard is damaged. Make sure you protect the computer from static and try to replace the battery again. If you have a Voltmeter you can check the voltage of the new battery, it should be around 3-6 Volts, usually 3 Volts, look what it says on the battery itself. If it shows correct voltage your motherboard is probably damaged.
If you have any questions or have some difficulties in handling your CMOS battery leave a comment and we will help you.
Use our forums to get help as well.
hello every one, i having problem with my pc. no beep, no post, its only a black screen when i open my pc. there is a power, the cpu fan is working. but i notice that the red led on the outside chasis is not blinking.
You may use our forums for this type of questions!
Give the specifications of your PC please.
Vadim
I have a toshiba satelite and it just turns off and if plugged in stops charging then when booted up it says cmos battery failure, what do i do?
My laptop won’t boot up…
It’s a GateWay MX6453. This problem has been of a progressive nature. It began with the screen flickering with black large square fields for a few seconds before turning all black and becoming totally unresponsive, and then, after a few more minutes showing a fixed pattern of various colors and symbols… This kind of crash would initially occur only occasionally, then daily, then a couple of times a day, all the time becoming more unwilling to boot up at all afterwards. Then there was a couple of weeks when I thought the problem was gone, but unfortunately it returned and within a couple of days it stopped booting up at all in spite of trying hundreds of times over several weeks…
All it does upon trying to boot up is beginning to light up a few of the blinking LED lights as it should upon a normal boot up, but within about 4 or 5 seconds this stops dead in its tracks and only the Radio On LED stays on, and, occasionally, a little backlight on the screen, but mostly not.
Now I’ve taken the PC all apart, disconnecting everything from the motherboard, even the CMOS battery, and the only difference I’m seeing is that the LED lights blink with a slightly different pattern before stopping, plus, one more difference, now all the LED lights turn themselves off within 40 seconds or so, faster for every boot up attempt, down to about 4 seconds, until I let it rest for a few seconds. Then, when I try again, I see the same pattern of ever quicker automatic turnoffs…
Well, that’s where I am at at this point of time…
Oh, I should mention that my HDD works fine on another identical laptop, while the HDD from that other laptop is experiencing the same problem once mounted to this problem laptop. Thus, I conclude that this is a hardware problem and not a software or virus problem. That is, unless the virus has attacked the BIOS???
Could this be a CMOS battery problem??? Or is it the motherboard, or what???
I’ll appreciate any help I can get in diagnosing this problem and fixing it…
Thanks for being there and doing what you do!
This problem of yours is not related to a CMOS battery or BIOS.
It is probably (99%) the video chip problem. What happened is one of solder BGA joints under the video chip got disconnected from the motherboard. What should be done is complete reballing of the chip and then reflawing (soldering it back) it. It is only done in the repair shop. We can do it as well but we are located in Israel.
Toda raba! Thanks ever so much for helping me with that diagnosis!
I’ve never been to Israel, nor do I know if I can ever get there given that I’ve rescinded all my State citizenships and all its associated Passports etc., which makes it kind of difficult to travel across some borders… But that’s besides the point!
What should I expect to pay for the job you are suggesting? What would you charge for fixing it and sending it back to me, if I were to mail the motherboard to you? And, would you happen to know someone near Sweden that are experienced and equipped to do such a job?
And, oh, I should mention that my CMOS battery is down to about 2.7 V. Kind of low, isn’t it? How low would it have to go before beginning to give me trouble?
Shalom,
Andy
Hi Andy,
you are welcome!
The battery replace after you fix the motherboard.
Just look on the Internet or go to some repair shops and ask who does reballing and reflow jobs. They should tell you.
You can do just reflow – it will be much cheaper and safer but the culprit can get back in few months, so if you decide to do just reflow they should give a worranty minimum for 9 months. The chances it will not break again after doing just reflow are 20%-30%.
There are much more chances (90%) it will not break again after doing complete rework (reballing and reflow) but it will be more expensive, we do it usually for $200.
Good luck.
pls iam having problem with my gateway computer CMOS battery that each time i replace with new one before 2 weeks it get flatten mean it run down completely and i have try changing the battery time without number i am tired so pls help
i have a pc of gigabyte 41 motherboard in which checksum or post cmos error occurs this results my pc to restart again n again i replaced the battery but no effect
I replaced the battery twice and i would function for two months. what would be the problem?
Hi, I have a Dell Dimension C521, almost 5 years old running Windows Home basic. I cannot get my puter to boot up, will not POST, nothing but the fan blows and light goes solid amber color and the dreaded black screen. I’ve heard it could be video card failure but I don’t even see a card hooked up, strange cause obviously it has to have one somewhere, but aside from that as a possible, could such a little thing as that battery (which I do see LOL) really render the whole computer useless like this?
Thanks…Candy
Nothing to do with the battery. It is probably the video chip.
When they say video card they mean video chip in the laptop.
The chip should get resoldered or better replaced.
i cant do reformat for my desktop it stops reading from the cdrom drive..do yoou think cmos battery affects it?
thank
i have my desktop pc with intel D945 motherboard having 1 gb ram, worked very well for last 4 years but last time when i switched it off and restarted it is not getting started and the monitor screen shows intel and press F2 for bios settings but nothing happens when F2 is pressed. When i removed d RAM THREE bEEPS were heard. i changed d ram but of no avail. I also checked its hard drive which is spinning n seems normal. All connections to motherboard are also o.k. Is this the cmos problem or any software problem………..
Plzzzzz guide………..
open CMOS battery from CMOS slot and do ESD(electro static discharge)and placed that CMOS battery in slot and switched on your system.
….and dont open other components(RAM, HARD DISK, CD-DRIVE etc) of your Desktop.
Hello, I have a HP DV3000 laptap with a CMOS battery CR2016. I tried to find one but got a CMOS battery for DV2000. Will it be okay if I will use the CMOS battery for DV2000 as a replacement for my CR2016? It has the same voltage 3v. Not sure if this will cause any issue on my laptap or distroy my motherboard in the long run. Need your idea on this case.thanks!
I have a gateway laptop, its always overheating, but that is not the main problem. My problem is that, my laptop’s time runs very fast, and whenever i turn it on time begins from 2007 and runs very fast. i think it have some BGA chips problem due to overheating. please help.
how i will change the cmos if a small metal sopporting to the cmos is broken.. will you help me please
I HAVE a Studio 15-i5 windows 7 laptop. Whenever i start my laptop after the dell logo comes erro window(black in color) comes and show “CMOS CHECKSUM ERROR” and when i RESUME or even change date or time ..i get some problems such as gmail,gtalk,etc doesnot open.
I m worried about how to tackle this and also Can I keep using the laptop by ignoring this problem as will the failed bios battery affects my other laptop parts in future…