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.
Need spare parts for your laptop?
If you are looking for spare parts for your laptop you can find brand new and used parts here. Just search by the part name and laptop model.
October 27th, 2009 at 8:07 am
Mario,
Take a look at this disassembly guide for a Acer TravelMate 3260 laptop, could be similar to your laptop.
By the way, it this model you can access the CMOS battery through the door on the bottom. It’s located close to the wireless card. Take a look at the picture in the step 10, it shows the battery.
I don’t know. Find the battery, remove if from the laptop, find the part number on the battery and google it.
October 18th, 2009 at 8:46 am
Hi,
I have a Acer Travelmate 4000 LZ1. I would like to know how to disassemble the laptop to get to the CMOS battery. Also would a Travelmate 3000 CMOS work in my Travelmate 4000.
I would like a service manual for a Dell Latitude C540/C64o laptop.
Your help is greatly appreciated.
Mario
October 18th, 2009 at 6:58 am
Furthermore to my question. Can i use a CMOS battery from a Travelmate 3000 on my 4000?
October 18th, 2009 at 6:53 am
Hi
I have a Acer Travelmate 4000 ZL1. Is there a guide so I can easily disassemble the laptop so i can get to my CMOS battery. Much appreciated.
Mario
October 17th, 2009 at 10:51 pm
john,
I believe in a Tecra A6 laptop the CMOS battery is soldered directly to the motherboard. Take a look at this guide for a Satellite M105 notebook. It has same body as Tecra A6.
In the step 22 there is a picture when the top cover is removed. On the bottom of the motherboard there is a square Intel chip. A little bit lower you’ll see the CMOS battery, it’s blue. Same as on 3rd or 6th photo in my post.
October 17th, 2009 at 10:43 pm
i have toshiba tecra a6. my laptop time isn’ running, i’ve checked the BIOS and it’ not running too. maybe i have a problem with cmos battery
do you know where the CMOS battery is?
and how can i remove it?
October 17th, 2009 at 6:40 pm
NovaScotiaMika,
I doubt that you can find just the battery alone. I think you’ll have to find and purchase the entire assembly.
October 16th, 2009 at 8:32 pm
I need to replace a battery that is encased in plastic just like the 3rd example (Dell). Can I buy the battery alone, or do I need to find the entire assembly – enclosed battery +cables+connector?
this is for an acer 9410.
October 1st, 2009 at 12:39 pm
ronin,
Have you tried that yourself?
I believe removing the CMOS battery will not clear the BIOS password on newer laptops.
September 29th, 2009 at 10:45 pm
Toshiba satellite M40X-148 cmos battery located under hardisk metal housing (the other side of motherboard). need to remove 4 screw tighten the metal housing (actually need to unassembled all parts & screw). it is soldered to the motherboard. need to flip the motherboard. half covered with blue plastic. short using wire the two solder for 15 minute and the bios password is reset. useful when u forgot the password.
September 28th, 2009 at 4:23 am
Think Maxdata CMOS battery to M350 Vision model with PhoenixNoteBios under keyboard is hidden in the back under screen hinge. Red & black wiring plus connector can be seen, and by lifting upper casing becomes visible in a spacing. Yet, battery underneath, requiring to lodge the part underneath the screen. The connector can thus be easily disconnected, but battery needs extra operations to gain access to.
September 18th, 2009 at 9:41 pm
how to delete the bios password?
September 13th, 2009 at 10:26 pm
bhagynath,
Not sure what’s going on but it’s possible you have some kind of compatibility issue between the PCMCIA card and your ThinkPad laptop.
I know that ThinkPads might now work properly with some internal Wi-Fi cards because it has to be some kind of “IBM certified card” or something like that. Apparently, the same applies to some external PCMCIA cards.
Can you find another PCMCIA Wi-Fi card for test?
September 12th, 2009 at 6:16 am
hai,,,im facing a big problem…my buffalo network adapter is not working..there is 2 PCMCIA slots in ma laptop..and wen i insert the adapter to the top slot ,laptop detects the network card but after installing the driver ,it says cannot start the device..and wen i insert it to the bottom slot..my xp gets stuck..my xp continues working if i remove the adapter from the slot..what should i do..im not able to use ma wireless these days…i am using IBM T21..
August 19th, 2009 at 8:19 pm
Tank,
Enter the BIOS setup menu and try loading default settings, there should be a button for that. After that save it and reboot the laptop. Not sure if it’s going to help but you can try.
August 19th, 2009 at 5:36 pm
the rtc battery went flat on my acer travelmate 520, and
as well as the date and time being lost, it also did
something to the graphics settings. I put a new battery in
and although the laptop works again, The acer welcome screen
(red satchel)is too big, when the laptop boots up the windows desktop is too big
(can’t see the start menu and systray)
If you hook up an external monitor that’s fine!
when this model was new, it was available with a range of screen sizes from 12.1″(mine)up to 14.1″. it’s almost as if it thinks it’s got the 14.1″ screen attached to it. According to acer
all models run the same motherboard, so how does the laptop “know”
how big its attached screen is?
I’m going slowly mad………
July 25th, 2009 at 9:16 pm
egyptian,
The CMOS battery is soldered to the motherboard. Take a look at this picture (motherboard from Satellite A105). You’ll see the CMOS battery on the right side from the circled screw.
By the way, removing the CMOS battery will not clear the BIOS password. If it’s your reason, don’t even try.
July 24th, 2009 at 4:11 pm
plz
can u help me
where is the coms battery in toshiba A100 satllite ??
ana how can i remove it ?
July 24th, 2009 at 5:55 am
We were discussing this over at the TechSupport Forums adn this post was pointed out. You mention that the RTC battery isthe CMOS battery – I understand this is not the case in all Laptops – they may have an DTC rechargable and a CAP or Flash Module to act as the CMOS Battery. This is due to the lowering voltages needed by the components on the MB – including the CMOS.
I happen to have an issue i’m attempting to trouble shoot – i noticed the time in the Bios does not keep time. But, not sure it it relates to the CMOS or if it does since i do not know if there is indeed a second soldered component acting as the CMOS battery (CAP or Flash) – my sytem OS keeps the correct time. IS it possible or one of the symptoms of a degrading Lythium RTC battery to cause restore issues or software running issues. My particualr issue is it seemingly starts to slow down to a freeze. After running tests known of my hardware aside from the lythium battery show fault or errors.
With todays comps – adn the possibility of teh dual RTC battery and other CMOS CAP or Flash – what are the symtoms caused by a bad RTC BAttery other than the time being incorrect in the bios? And how do you know if you have the Dual battery/CAP? Most Manufacturors will not give up service manuals which show components soldered to the MB.
July 17th, 2009 at 10:09 pm
billh,
Take a look at this disassembly guide for a Toshiba Qosmio F25. Could be very similar to your Qosmio F20.