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
149 Responses to “CMOS battery also know as RTC battery”
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Pages: [6] 5 4 3 2 1 » Show All
April 25th, 2013 at 7:41 am
Hi Mr. Repair-man,
my laptop was Toshiba Satellite C800D which has RTC battery like picture #4 only it placed near the HDD slot, not near/around RAM slot.
i had these problem, supervisor password which i don’t know. i had try the software but none of works. so now i try my self to do the hardware way.
first, i just unplug the cable (black-red) for about 15minutes, and then plug-in. turn on the laptop and enter the bios. the timer was resetted, but not with the supervisor password (the password is still on it).
so, is it the right thing to remove the RTC from the mainboard along with the cable, and also the other stuff such as battery, RAM and HDD also being removable??
please help me.
thank’s
April 7th, 2013 at 12:17 am
Hi Repairman
I had the same symptoms as Diztek (number 17) with the Satellite 1130 switched on, a quick whiz of the hard drive, nothing on screen then the little devil powered off.
Reading your suggestions to Diztek, I first found the two wires in the memory compartment, shorted them to see if the bios changed, nope. But then I removed one memory dimm and lo! the Sat started first time, and every time since. Great stuff, thank you so much.
Misterfish
January 20th, 2013 at 9:29 pm
Hello. My toshiba a505 s6005 recently started showing the cmos battery failure error message upon start-up. Do you know if this model’s battery is soldered on?
July 24th, 2012 at 1:37 pm
My laptop (hp dm3 entertainment)keep making a beeping noise (not from the speakers)at random times. mostly just a single beep sometimes a triple. could this be the rtc battery dying? i checked the main battery it’s fine i also ran checks on the hard drive and the memory they both passed, and i removed and put back in the memory and hardive as well and it is still doing it.
July 5th, 2012 at 5:03 pm
i have a problem with my old laptop, sony vaio vgn-fs790. i don’t know about my bios date, but my bios time is not moving(the seconds). don’t know if it’s time for me to change my cmos battery because of it. whenever i boot up to windows, it’s not giving me the correct time & date. or maybe.. something’s wrong with the bios..when i acquired this(bought it cheap), it has an updated bios, as what i saw in the sony website.
June 13th, 2012 at 8:32 pm
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.
April 22nd, 2012 at 2:15 pm
I have a Toshiba Satellite L305D-S5928. A few days ago my computer just had a shit fit. The sound would go wonky, video playback was having an issue. I updated some things then rebooted the system… it wouldn’t go into POST on the BIOS. I tore apart the laptop and examined everything, looking around at the batteries and processors. Making sure everything was plugged in, it was all good. I put it back together and booted up the computer, it started up fine but I got an error about a faulty CMOS. Okay… I went through, examined everything driver wise. Updated some things that were out of date. Restarted the system… black screen again. No POST, nothing. Lights are on the front, fan is running. Bricked computer. Please tell me it’s just the CMOS RTC battery.
March 24th, 2012 at 7:24 am
Hello, this is the second time im going to post my question, where can i find the cmos battery on my NEO M545G laptop? The 1st one i posted was some how deleted from the threads. tnx
February 9th, 2012 at 2:23 pm
ya intente quitando la bateria y no me funciono,
service FW2YYJ1-2A7B
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?