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
December 15th, 2011 at 11:08 am
@ Basel,
I don’t remember off the top of my head but most likely this laptop has two CMOS pads in the memory compartment. You can find them when both memory modules removed. You short those pads with a screwdriver and it should clear the BIOS password.
Removing the CMOS battery will not clear the password.
September 14th, 2011 at 12:34 pm
hi i have Toshiba sattelite A300 I forgot BIOS password how i can remove it
September 7th, 2011 at 12:03 pm
Just wondering if anybody knows the cmos battery needed for HP ZV5460US, SN CND592169H, SN OR471UA #ABA, Motherboard 370493-001, EHR66A1
August 31st, 2011 at 6:13 am
Hi, I have a Toshiba Satellite L45-S7409.
What kind of CMOS battery do I need?
every time I turn on my laptop I have to press F1 key to continue and set time after login to windows.
August 16th, 2011 at 9:34 pm
@ Corey Perry,
Not sure 100% but I think removing the CMOS battery will not clear BIOS password. Most likely this one is like previous Satellite models – there are two contacts on the motherboard that you have to short with a screwdriver for a few seconds. Usually these contacts look like engaged gear teeth. Maybe you can find these contacts in the memory compartment. Just a guess.
August 16th, 2011 at 8:28 pm
I Have A Satellite u505-s2950 (Very Similar Design As In Picture 6)and im wondering if I unsolder the cmos battery will it remove the password or is this one of the laptops that that will not work for.
plz help
June 18th, 2011 at 4:08 am
Will a Toshiba Satellite laptop operate without the CMOS battery?
June 5th, 2011 at 4:56 am
04 toshiba satellite a25 must disassemble every thing screen harddrive key board i hope i can remmember how too put it back togeter 83 screws out so fare 18 screws to go CMOS/RTC GREAT DESIGHN what a load. seems i could be more execesable tashiba support didnot know where CMOS/RTC WAS REFERD ME OUT SAYS TECH SUPPORT 34.95 PLEASE.DIFFACULT, SAY A PRAYER FOR MY LAPTOP.AT FREE I PAID TOO MUCH. STEVEN
May 1st, 2011 at 12:22 pm
How can I clear the bios password in a dell inspiron 8100
service tag # 5nppy01-595b.
March 29th, 2011 at 9:57 pm
Good day mam,how can I identify the cmos battery code of my neo laptop M541N,co’z I dont have any model of it..thanks and hope that you may provide my query..
March 19th, 2011 at 6:30 am
Please, can some one tell me how I can locate cmos battery for comaq R3000 model R3360US. I have opened the laptop but just could not loacated. I can not access my laptop since it asks me the power on password and i just dont have any idea what it might be. I even can not remeber that I have provided one for my laptop. Please help.
March 18th, 2011 at 2:26 am
hi,
where is the levono ideapad y430 cmos battery located!? i have tried to search the net for it and still not successfull..the only results i get are of sony, hp, compaq etc, but NO LEVONO! Please help
Thank you
March 7th, 2011 at 12:24 am
Hello repair man i bought this laptop used and did not notice that it needed a boot password i can not load into anything not even to load a windows disc the labtop is Compaq nc6320 ive tried to hard reset the machine (taking the rtc battery out) it does not work, can this be possable because the rtc battry is dead for it not to clear bios
March 2nd, 2011 at 8:53 pm
Kim,
I’ve seen this problem on more than one Toshiba model. One day it’s just setting the BIOS password on its own. I think it’s faulty BIOS.
You can try this. In the memory compartment search for two pads marked as B500. Short this pads with a screwdriver and turn on the laptop. Keep this pads shorted while the laptop turning on. If it’s successful, the laptop will bypass the password screen. If it doesn’t work, try again until the password erased.
After the BIOS password cleared, update the BIOS to the latest version.
March 2nd, 2011 at 8:25 pm
T,
Just desloder the old battery and solder a new one.
I think this Maxell ML1220 CMOS battery might work.
February 28th, 2011 at 7:14 pm
At my office I have a Toshiba Satellite L305-S5955 I never set a password but now i can’t even get into the bios it asks for a password how do I bypass this (if it is taming out the CMOS could you give me a Link to a pic so I can see what it looks like I took the entire thing apart and I don’t see anything that resembles a battery. Toshiba wants more $ to fix it than I paid for it brand new! I will never by another Toshiba this is the 2nd time that it has done this the first time was 3 months after the purchase date!) thank god for factory warranties. What brand would you suggest for my next purchase?
February 25th, 2011 at 12:45 pm
Hi Repair-Man,
I’ve got a bad RTC battery in a Toshiba A215 that is only 3 years old. I have tried charging it, updating the BIOS, all kinds of other possibilities, but to no avail – battery errors keep coming. The next step is to try changing the RTC battery. My friend who is skilled with laptop surgery says he’s willing to try to replace it for me. Any tips for how to deal with the soldered-on battery that this model has? Thanks for your very helpful site! –T
February 24th, 2011 at 11:38 pm
How can i reset bios password for acer aspire 2920, i’ve tried to find CMOS Battery but i can’t found?
February 17th, 2011 at 12:52 am
i have a sony vgn-n35o3 and its asking me for my bios password and i forgot it. i tried unpluging that little battery but it still ask me for the bios password. what could i do?
February 16th, 2011 at 11:12 pm
kusun,
I don’t think this is CMOS battery related problem.
Did you test the AC adapter? It’s possible the adapter is dead and the battery doesn’t have enough charge to start the laptop.
Test voltage on the AC adapter.
February 16th, 2011 at 11:09 pm
NLJ,
Sorry, I don’t know this model at all.
February 15th, 2011 at 8:50 am
Hello,
I have HP Pavillion laptop.
Just two days ago, it stopped working suddenly. I turned on the power button, but the laptop keyboard lights up for 1 sec, then goes off. Same thing with and without battery (only with power adaptor). Is my CMOS bad? what do u think? Thank you very much.
February 13th, 2011 at 1:05 pm
Hi
Please can you tell me where the rtc battery is located on the Toshiba Portege P7220?? (exact model pp722e-h390q-en)
Thanks
NLJ
January 31st, 2011 at 5:44 am
uhmmm… ill try.. there are two.. the problem is the other one is below the keypad.. so i must open them whole.. i’ll try.. thanx so much!!
January 28th, 2011 at 4:42 pm
JohnPercy,
Could be memory failure. Try reseating memory modules.
Do you have two memory modules installed in the laptop? One of them could be bad. Try removing modules one by one and test the laptop with each one separately. When the bad module removed, the laptop should start properly.