CMOS battery also know as RTC battery
Any laptop computer has a CMOS battery also known as RTC battery. The CMOS battery connects directly to the laptop system board and helps to retain important BIOS settings such as system time, date, BIOS configuration while the laptop is turned off or even when the main battery is removed.
The CMOS battery is rechargeable and it’s getting charged when the laptop is plugged into the mains.
CMOS batteries come in different shapes ans sizes.
On the picture below you see a basic coin cell CMOS battery. This type of batteries usually found in older laptops. This battery is removable and replaceable.
Here’s another type of CMOS battery. Basically, it’s two coin cell batteries but they are bundled together and have a cable which plugs into the system board. This battery is removable and replaceable.
On the next picture you see a CMOS battery which is soldered to the system board. In order to replace this type of battery, you’ll have to unsolder it from the system board.
CMOS BATTERY LOCATION IN A LAPTOP.
In some laptops the CMOS battery could be easily accessed from the bottom, as it shown on the picture below. As an example I took a Dell Inspiron 1720.
In some laptops the CMOS battery is hidden under the keyboard. As an example I took a HP Compaq nc6400 laptop.
Here’s the worst case scenario. The CMOS battery is hidden under the laptop cover. In order to access and replace the battery you’ll have to disassemble the whole laptop. As an example I took a Toshiba Satellite A305 laptop.
CMOS BATTERY RELATED PROBLEMS.
Here’s the most common problem related to the CMOS battery.
Each time you turn off the laptop it resets date and time back to factory defaults. When you turn the laptop back on it asks you to set date and time. If that’s the case, most likely your CMOS battery is old and has to be replaced.
By the way, removing the CMOS battery on most newer laptops will not clear the BIOS password.
Laptop parts | Repair Man | 
December 26, 2008 3:04 pm
140 Responses to “CMOS battery also know as RTC battery”
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Pages: « 6 [5] 4 3 2 1 » Show All
January 28th, 2011 at 4:17 pm
natakilub,
Are you sure the model number is correct? I google your model and didn’t find any laptop.
January 28th, 2011 at 4:15 pm
Leonardo,
I’m not sure about this particular model but let me guess…
I many newer Toshiba laptops the CMOS clear pads located in the memory compartment (sometimes you have to remove clear film or sticker).
Usually, these pads look like small engaged gear teeth.
You unplug the AC adapter, remove the battery and short those pads with a screwdriver for about 30 seconds.
After that assemble the laptop and turn it on.
January 17th, 2011 at 2:34 am
Sir, my laptop,(compaq presario r3000) starts to shut down before it turns on the screen…the keyboards lights though before it shuts down.. the charger seems okay, but when i used another charger with 19V (the original one is 18.5V) it boots up the screen but then again, it shuts down after 3-5 seconds.. the cycle repeats.. can you please help me? it does not have any batteries since they just gave it to me..my friend says the CMOS batt must be replaced.. some says its the harddrive.. please help me.. repairs in my country is reaaalllly expensive.. help.. thanx so much…
January 14th, 2011 at 2:22 pm
Hello there, any knowledge where i can find bios battery on neo sony empriva nx40 laptop?
January 13th, 2011 at 6:47 pm
How can I clear the BIOS password in a Toshiba Satellite L505-S5984?
January 9th, 2011 at 11:01 am
disassembler,
I don’t think this is CMOS battery related issue. I think the laptop should turn on even if the CMOS battery completely dead. It will not be able to keep current time and date, but should turn on. I think you have another problem.
First, I would check memory modules. It’s possible one of the modules is bad. Try reseating memory. Try removing memory modules one by one and test your laptop with each module separately.
January 9th, 2011 at 12:29 am
I have a vaio vgn-s360. When I turn on the power the lights for the indicators (battery, power, system) and the fans turn on but the monitor is blank. So I try plugging in an external monitor and still see nothing. Is this a problem with the cmos battery? What can i do??
January 7th, 2011 at 9:20 pm
Adam,
What HP laptop? What model?
Also, how does it fail? Do you get any LED light when laptop turned on? Is it dead completely? More details please.
January 6th, 2011 at 12:13 pm
i have a HP laptop that will not even load the BIOS settings do i take out the CMOS battery
January 4th, 2011 at 8:53 am
Dar,
This is a desktop PC right? The CMOS battery should be somewhere on the motherboard.
December 31st, 2010 at 3:07 pm
hi,
Where can i see my CMOS battery in my ASPIRE AX1800. i forgot my
December 7th, 2010 at 11:16 pm
Tobey,
Could be memory failure.
Do you have two memory modules installed in the laptop? Try removing them one by one and test with each module separately.
Also, I assume it’s not just failed power supply. Right?
November 18th, 2010 at 7:15 pm
THANKS!!!! it worked!!! gotta give it to ya!! You are truly the REPAIR MAN thank again
November 18th, 2010 at 8:36 am
trashman,
It’s not necessary to disassemble the laptop. Try this method: http://www.laptoprepair101.com/laptop/2006/02/10/remove-clear-toshiba-laptop-bios/
It works for most older Toshiba laptops.
November 17th, 2010 at 11:21 pm
hello
i have a old toshiba tecra te2100 i forgot the bios password. i tryed removing the cmos battery for to dats but no luck i called toshiba and they want me to send it in.$400 bucks to fix he said!! does anyone have any ideas? or can you tell me where the bios chip is located on this type of motherboard?
November 17th, 2010 at 1:52 am
I was watching a movie yesterday, and my laptop went suddenly hung… I had to pull the battery out to get it to work, then when I put it back on it didn’t come on not even the BIOS, the screen didn’t even light up, could this be CMOS or???
November 15th, 2010 at 8:33 pm
Tom,
First of all, try reseating memory modules. If you have two modules installed, remove them one by one. It’s possible that one of the modules failed. When you remove the failed module, the laptop should start properly.
November 15th, 2010 at 8:29 pm
hardx,
If the laptop video failed after updating the BIOS, there is a chance that BIOS got corrupted. If that’s the case, you’ll have to replace the motherboard. I REALLY doubt that removing the CMOS battery will help. By the way, the CMOS battery is soldered to the motherboard.
Here’s what you can try.
Turn off the laptop, disconnect the AC adapter and remove the battery. Wait for a few minutes. Now plug the AC adapter and try tuning it on again.
Also, try reseating memory modules. Just in case.
November 14th, 2010 at 12:25 pm
i have a toshiba a215, my laptop turn on but the screen is black its happened after a bios update, the cmos battery is like the last pic so remove the battery will repair my laptop? and how i can remove the battery or reset the bios?
November 10th, 2010 at 8:10 am
My Toshiba L355D is dead – nothing but the DVD spins (no HD action) and screen is blank), This happened after a couple of days of lost time/date. I replaced the CMOS battery and still get the same deadness. Any suggestions?
Thnx, in advance,
Tom
October 19th, 2010 at 7:01 pm
Hi Repair Man
i have an old compaq evo n600c that has not been used for a while the main battery is dead i only used ac power when working on it.
A few days ago im tried to boot the laptop. Im getting an error message system disk error/non system disk…
So what i did i removed the battery and booted from the ac power.
I received a message 162-system not defined…
So the system downloaded default settings
and prompting me to select F1 saves changes F2 ignore changes
I also see a message CMOS checksum invalid.
the hard is also doing a clicking sound
Any help will be appreciated thank you
thank you in advance
October 14th, 2010 at 11:49 am
it could be that I meant cmos battery. Its just that the clock stops if the laptop is not on mains power. If i leave for a few weeks then it will refuse to connect to internet unless I system restore and reset time and date !!!!
October 14th, 2010 at 11:42 am
Hi, any idea where i would find the bios battery on a sony vaio pcg-791m? do i need to completely dismantle the thing?
Kind regards
October 13th, 2010 at 9:03 pm
Thanks Repairman, you are a legend..
October 13th, 2010 at 7:33 pm
barbara,
I think on some older laptops you can remove the BIOS password by disconnecting the CMOS battery.
I’m not sure 100% if it will work but you can try.
Turn off the laptop, unplug the AC adapter, remove the main battery, disconnect the CMOS battery and wait for about 10 minutes. Press on the power button while all batteries removed and keep it pressed for a seconds.