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.

Coin cell laptop CMOS battery

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.

Removable laptop CMOS battery

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 soldered to motherboard


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.

CMOS battery accessible from bottom of laptop

In some laptops the CMOS battery is hidden under the keyboard. As an example I took a HP Compaq nc6400 laptop.

CMOS battery under keyboard

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 under laptop cover


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.



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  1. 147
    Heather Says:

    Any idea where i can find a replacement cmos/rtc battery for a Toshiba Satellite A505-S6965 PSAP3U-01G00C ? I’ve looked everywhere, can’t find specs or anything on it, it’s soldered to the board.


  2. 146
    David Says:

    pls i hv laptop toshiba dynabook TX/470LSE1 and when i on the laptop it showns me password up at the rightside hand of the screen i think is Bios password, pls how can i remove it from the system board i need your help. thank you

  3. 145
    onejohn Says:

    hi repairman,
    i have the same battery as in pic3,
    do you know where i can get a new one? if not a simalar type
    thanks john

  4. 144
    deim Says:

    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.

  5. 143
    Misterfish Says:

    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.

  6. 142
    Philip Says:

    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?

  7. 141
    bill Says:

    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.

  8. 140
    roy Says:

    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.

  9. 139
    sandip bamdale Says:

    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.

  10. 138
    VezRoth Says:

    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.

  11. 137
    jovy monasterial Says:

    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

  12. 136
    DELL latutud e5400 Says:

    ya intente quitando la bateria y no me funciono,
    service FW2YYJ1-2A7B

  13. 135
    Repair Man Says:

    @ Basel,

    i have Toshiba sattelite A300 I forgot BIOS password how i can remove it

    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.

  14. 134
    Basel Says:

    hi i have Toshiba sattelite A300 I forgot BIOS password how i can remove it

  15. 133
    Kathy Says:

    Just wondering if anybody knows the cmos battery needed for HP ZV5460US, SN CND592169H, SN OR471UA #ABA, Motherboard 370493-001, EHR66A1

  16. 132
    navid Says:

    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.

  17. 131
    Repair Man Says:

    @ Corey Perry,

    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.

    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.

  18. 130
    Corey Perry Says:

    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

  19. 129
    Rick Says:

    Will a Toshiba Satellite laptop operate without the CMOS battery?

  20. 128
    STEVEN Says:

    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

  21. 127
    Amaury Lora Says:

    How can I clear the bios password in a dell inspiron 8100
    service tag # 5nppy01-595b.

  22. 126
    Joemar Cera Says:

    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..

  23. 125
    fredi Says:

    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.

  24. 124
    Imran Says:


    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

  25. 123
    Chad Says:

    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

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