Why Do Motherboards Have Batteries? 

I remember wondering how my PC keeps time after I power it off even though I didn't have internet back in late 2000's and my friend's dad told me about this little battery

We have had to replace a fair few CMOS batteries over time. The last one was a couple of months ago on my dad's gaming laptop from 2016. It started loosing it's timing and knew it was time to get a new battery. People may think it is a minor issue. But it can drive you crazy. Especially when you have to manually keep resetting the time so your certificates for things work. Having it keep coming back on saying it was nearly 100 years in the future, caused the pc to have a fit with the certificates saying they had all exprired. Which meant I had to fight with times for at least 5 minutes to get things set right everytime this happened. Not my idea of fun.

This answered a question I've had for half of my life; "how do devices keep time when turned off". I figured there must be some sort of power source still going. I'm just new to PC hardware so I didn't know that motherboards themselves have a battery in them for that reason.

Nice video. I'd have liked some mention to laptop nvram chips and how the absence of a default "clear BIOS settings" mecanism in laptops can turn into a real hell if you need to enter the BIOS of a password protected laptop.

At times even the clear_CMOS button/jumper fails to function in a thorough manner, never assume it worked properly. Removing the battery is still the only sure way to reset EFI settings in a thorough and reliable way. I don't know why, but my guess is that EFI initialization crashes or freezes in such a manner that the clear_CMOS jumper/button cannot obtain access to clear whatever errored bits crashed the EFI. Perhaps certain specific EFI settings bits relay power or interfere with the relay of power? Would be interesting to get an answer to this from an engineer at American Megatrends.

My first IBM-compatible PC, a Tandy 1000, did not include a battery. There was no built-in timekeeping, and no BIOS settings. For timekeeping I needed an ISA expansion card (with its own battery), which also upgraded my RAM from 128KB to 640KB. The '80s were fun times. 🙂

its so fascinating how long the battery lasts... i have never seen even the oldest motherboards... and they STILL work.

Techquickie: Why Do Motherboards Have Batteries? Everybody: The user manual says so!

3:04 Saying NTP is not used for home PCs is completely wrong. Every PC out of the box is configured to use NTP. This is standard on Windows, Linux, and macOS. This is one of the key parts of specifying your location during setup of the OS/user settings. For Windows, the default NTP server is likely set by default to "time.windows.com" which is of course, Microsoft's time server. However, you can specify your desired time server manually, and if so inclined, serve your own time via an NTP server. The point of having an RTC (real time clock) battery is to allow functions such as "wake by RTC" if you have a system which you want power on automatically at some scheduled time, run some task, and then maybe shutdown afterwards, keeping energy usage to a minimum. Another use for it would be to remove the requirement to have internet connection to keep some form of time. Some form of time sync is important if you want to avoid having to manually make adjustments to your clock for things like DST, time zone changes while travelling, or jitter (which means that your local clock is non-ideal and typically will be comprised of some amount of "periodic jitter" meaning it will be consistently slower or faster than the perfect clock).

I once got this 386 workstation, with all the things attached to it, including an IBM Proprinter-I, rather blocky mouse, and things like that for free as that thing had been just sitting in a corner for quite some time. For most parts everything was in perfect working order... But the lithium metall (!) battery was dead. You could still use it, as long as you would just set all the drives... As back then stuff like clock speeds and multipliers were mostly set by jumpers, but plug & play sort of hard drives didn't exist... But it was fairly simple to do, especially after doing it a couple of times. I could actually do all the settings and get DOS running in less than half the time it took for modern computer (at the time) to load Windows. But usually I didn't bother setting time and date, so that old computer was usually re-living 1988, I don't really know why did it allways return to that specific year, but it soon became a part of it's whole being... Being such an old computer, having a slight case of dementia didn't seem that wrong. After all, I did use it for some classic games or tinkering a little something with QBasic, all a bit 1980's sort of things to do... Although might be that the computer didn't see my games as very "classic" or "retro", allways thinking it is still 1988, but the point was to have fun and that we had.

many computers except tablets and phones which are SBC based have a CMOS battery that not only keeps time but also in some cases keep the TPM chip settings saved. This means that taking out the CMOS would reset the bios completely as it was even before OEM setup.

As a repair technician, swapping cmos batteries has fixed a lot more laptops than I would have ever expected when I started.

I like how there's always something to learn from these videos, even when I feel like I already know the topic. You do a really good job at educating people new to PCs while also giving experienced people an interesting fact or two. I always thought that telling people to reset their CMOS was a bit stupid, because the people asking for help in situations like that are often new builders who have no idea what that means. Now I know that it's stupid for another reason. The BIOS isn't even stored on the CMOS chip!

Thanks for the update. I am a PC tech but not really looked into this topic as it seem to have not changed. Which I think was a win for manufacturing.

In the early ’00s and 90ies switching this battery sometimes was a magical fix for weird problems (such as random shutdowns, temporary black screens etc) in old systems. Which begs the question if low voltage on this battery could cause unexpected issues in miscellaneous subsystems or if removing it just blasted some bad setting in CMOS or similar.

I've had a fair few CMOS cells run out on me in my time. I tend to keep computers long enough that this becomes a concern. My old gaming laptop needs one, and the last laptop I had open for a general service got a new one out of precaution. Click below the fold for a history lesson and personal anecdote. Fun fact, waaaaaaaay back in the old days when processors were known by numbers, our CMOS batteries were NiCd! Because we didn't really have lithium cells yet, and physically couldn't store a long amount of power on the board. So MB manufacturers just *recharged* the battery whenever the system was on. These PCs would lose their settings within a few months to a year if you left them powered off. You could buy an alkaline battery pack to connect to an external jumper, that would last ..... I think mine made 20 years before running out? I upgraded it to a lithium coin cell. These things have since just become motherboard murderers though, as any motherboard old enough to still have a NiCd CMOS battery is also old enough for that battery to have failed and begun leaking caustic substances, corroding away traces rather rapidly. Both my 386 and 486 motherboards have had this happen, as has my Amiga 500's expansion RAM card - the 486's battery having even *exploded* before I got the PC! I had to solder new wires on my 386 to repair it (Try that with a modern board...), and the Amiga RAM card needs .... a lot of help. Though I do have a very late model 486 motherboard with a coin cell, so you aren't likely to encounter one of these relics of computing past unless you're truly passionate about retro computers. And if you do happen across one, get with somebody who knows how to solder immediately to have it removed or replaced! Also, recycle the old battery properly. Cadmium is nasty stuff. --- NEVER directly replace a NiCd with a lithium coin! The charging system is still active, and will quite happily explode your brand new coin cell, possibly taking your antique computer with it. Consult your motherboard's manual or other resource to locate a jumper to disable the charging system before installing a non-rechargeable battery. You may need to just wire it in to a separate jumper header intended for the purpose...

Probably worth mentioning that a lot of security, encryption, and login stuff nowadays absolutely requires correct time. A lot of keys that are generated have a time-based element to them or have expirations. If you're having weird login or security issues, check your time! If your time doesn't stick after reboots or drifts, check your CMOS battery!

That clock battery is actually the way most old games used to save or even keep track of time as well, not just PCs. Pokémon Gold/Silver/Crystal was probably the most popular example of the latter back in the day, having a full day-night cycle that depended on the time you put in at the start of the game.

Not all computer motherboards have used or currently use a button cell battery to maintain the CMOS/clock settings, especially earlier PC’s, Macs, and certain other microcomputers. For those computers that had an on-board CMOS/Clock to maintain, some used small tube-shaped 3.6v Lithium 1/2 AA batteries. Sometimes the CMOS battery was soldered onto the motherboard though iusing battery holder so you couldn’t just pop the battery out to replace it. Sometimes laptops used a button cell shaped battery that had wires soldered to it then soldered to the motherboard though again of you were lucky it used a connector so you could easily unplug the battery to replace it. I suspect that in some cases the manufacturer never expected the machine to in use long enough to need to replace the CMOS battery so they simply soldered it on. It seem that at some point, PC motherboards seem to have coalesced on using button cell batteries in holder that allows for easy replacement of the battery when needed. Soldered on batteries are a particular problem for retro computer collectors as the batteries will eventually leak and damage the motherboard due to the battery acid. That’s why if you have an old computer with a CMOS battery that has yet to leak and your storing the computer away, or it’s the battery is simply old then you should remove the battery to be safe. If it’s soldered on then desolder it and replace it with a battery holder that allows you remove the battery when storing the computer away and to make it easier on yourself when replacing later on. Always replace very old batteries on old computers with new one regardless since you never know when they will start to leak and they will leak at some point, mark my words. .

You should remove the battery from your computer if you're thinking on storing it for a long time, and if you bought an old computer that has it, you should check it up immediately. After many years, they tend to leak badly all over your PCB.

Heh, quite a fair amount of motherboards these days, like ASUS hide the CMOS battery behind fancy panels, making it a nightmare to remove if there's a reason to do so.

I once had a coworker forget their BIOS password, it was amazing how easy it is to remove that battery, wait half a day, and log back into a computer bypassing the password. Physical security is real 😢

If you have an old Apple Macintosh you might run into a tricky battery problem. It's been a long time since I handled one of these so I can't remember the model. Thing is the machines power button was on the keyboard. But it wasn't powered by standby power like they usually are on a PC, but instead there were a lithium cell inside the keyboard. If this ran dry then you couldn't turn on the computer. I had a customer bring in one of these when it refused to start. We didn't work on Apples machines but he asked us to take a look. My colleague opened up the keyboard to see if the switch might be broken and he was pretty surprised when he found a lithium cell inside. When it measured in at about one volt he replaced it and suddenly the machine worked again. Another fun thing was that the motherboard in this Mac was manufactured by LG-Electronics, or if it was still called Goldstar. Actually that might just have been the PCB in the keyboard that was made by Goldstar. It's been so long I can't remember. I do however know that a portable Mac (PowerBook 100 or possibly 140 - 180) was manufactured for Apple by Acer.

NTP is *DEFINITELY* used on home PCs. What do you think is happening under the hood when Windows synchronizes the clock with "internet time" Plus. Many servers do still keep an internal clock and a battery, but NTP time is preferred, with local time being a backup source.

last month i had to replace two bios batteries in our working stations from 2012. apparently the bios battery also controls (gives current/voltage to a) chip which is used for coordinating usb devices and the boot order. this results in an error that the pc trys to boot from any usb device, be it a mouse, stick, or keyboard. -.-

Funny story… back in 1994 I was driving from Chicago to Minnesota, during a blizzard, during spring break. The cell phone my parents gave me for emergencies rang. The emergency? The cmos battery died on our home computer and I was the tech support. My dad thought it was my fault, argued with me until he heard me yell “Oh Shit!” Three times. I crashed into a side rail because of the snow. Fun times. No one was hurt except the turning light on the front right of my ‘81 Toyota Tercel.

Back in the 90s my dad use to have a "security password" so I couldnt play when he wasnt home, and I discover that removing that will remove the password, but the time too, but I figerit out and chage it back. I was like 8

Great video as always! The more we know: Answering questions I’ve always wondered but rarely asked.

4:13 anything for you, Riley boy! _Pegasus' voice_

love the stock footage of the servers having lights resembling the x360.... hope they dont red ring! :)

128 bytes isn't always 128 characters. I would add ASCII before characters because a Unicode character may not be one byte. Hence why low level languages handling strings are scary sometimes as you can incorrectly address the string a way it wasn't meant to be read.

I can tell you first hand what happens when the battery goes bad. Random BSODs and weird BIOS behavior like it doesn't save settings yet doesn't tell you so. Very hard to debug, but easy to solve.

Man, I'm so glad LTT ppl do 2k videos. Recently bought a 2k monitor and looking at a 2k video footage right after a normal 1080p one makes the difference really noticeable.

It really sucks when your CMOS battery dies and you can’t boot into your PC anymore, but aren’t sure why. Took me hours to realize that the CMOS battery was dead, and that the issue was in the BIOS settings.

had to use the old "remove battery to reset bios" trick just last year! didnt know its just for keeping time now. realy glad it still worked!

I love Riley & James sooo much, you guys bring value to LTT

The statement at 2:52 is wrong. Windows and Linux use NTP to keep accurate time. It's not just servers that use NTP. Desktops and laptops use it too. Also, servers still have CMOS batteries (at least the HPE ones I've worked with for many years do). The BIOS in servers does not use NTP. Most of the time, you just allow the host OS (Windows Server, Linux, VMware ESXi, etc.) to set the time. The OS will adjust the RTC (real-time clock) -- the circuit that needs power from the CMOS battery to keep incrementing the time while the computer is off. NTP is necessary no matter what because the RTC is not accurate. The time kept by the RTC will drift over time, so computers need to query NTP servers because the NTP servers get their time from atomic clocks. Atomic clocks are far more accurate.

I actually wrote my current RAM timings into the XMP profile, that way if I ever have to replace the battery or even the whole motherboard, I can just enable XMP and it's back to normal

The CR2032 in my copy of Chrono Trigger is 25 years old. And it's held the save data all these years. My best guess is it's easier for such a battery to simply hold data in place than it is for such a battery to run a clock for upwards of a decade.

I’m building my first pc and my motherboard arrives today. I love these videos

There's a bit of not quite accurate stuff when talking about NTP. - First of all typically NTP is used to handle time drift, and most servers will not use it to set the clock outright but instead use it to correct drift regularly, on many systems, particularly linux, the default settings will not instantly set the clock if it is way off (for example if it was set to December 31, 1969 as used to happen when CMOS was cleared, or if it was just stuck on the last time the power was on) but instead will gradually adjust the clock until it matches, this is to prevent time based scheduled tasks from happening in too unexpected of an order by the clock randomly changing significantly. - Also, you said that NTP is not used on home PCs, but actually, most home PCs do in fact use NTP to synchronize their time.. Windows has had NTP updates as part of their time settings since as far back as Windows XP (back then it was off by default but on modern Windows 10 and Windows 11 it is on by default). Windows NTP settings (which can be found by right clicking the clock in the status bar) is set to the NTP server of time.windows.com by default. - Macs also defaults to having "Set date and time automatically" checked in Date & Time preferences, with a default NTP server of time.apple.com. In both cases or on *nix machines, you can easily change these NTP servers to any other NTP server, useful if you want to actually run an ntp server inside your network and have all your other computers synchronize to use it as a master time for your network. Linux based NTP setups even let you synchronize both ways, synchronizing itself to a master clock elsewhere (I typically use time.nist.gov cause I like the idea of synchronizing to the National Institute of Standards and Technology), and also providing a master time for your network.

That subtle flip so Riley points the right way is pretty funny.

Thankfully my CMOS didn't clear when I removed my CMOS battery but an easy way to know it's time to replace it is when your PC starts losing time (especially if you have it set to not fetch time from the internet). You'll first notice this when a program breaks or a browser page or log in something doesn't want to work. After 7yrs of service, mine was due.

After a power outage my PC would not turn on (power button did nothing), yet the MOBO leds worked fine / power supply did not smell burnt. I was thinking of getting a new PSU since I had no idea what the issue was. Turns out that, on my ROG STRIX Z370-G mobo, if the cmos battery dies... the power button will simply not do anything. Glad I tried swapping the battery, before I got a new PSU.

Dell nowadays use cheaper battery for the RTC. In the 2010-2015 models the battery is 10 years plus life, but since 2016 it runs out juice just after 4-5 years.

My motherboard (ASRock B550 Phantom Gaming 4) actually has two pins on it called a "CMOS Jumper." Basically I just touch them with a flathead screwdriver, and that resets my BIOS. I had to use it while I was initially building my computer because it wasn't booting correctly. Which is good, because I found the CMOS battery on the board pretty difficult to remove.

I hate that companies keep old crap just because that is how it WAS done. If you buy a product and don't even skim through the manual, you are wrong. I used to be on the team of learn to use and now that I know it shouldn't change, but that has drastically changed after I went to company that offered SOOOOOO much more stuff for a product. I bet most people don't even know that their newer products has a wireless connection available for support. Recently bought a new place and had to buy a washer and dryer,. Most had some sort of quick support built in that told the user the issue with a phone, not to mention the features for security prevented things like poor exhaust from causing a potential fire. Then we get to fridges, the 7 year old fridge left had a few things that failed, which it told me from a sensor (after I read the manual of how to diagnose) that basically told me it was cheaper to buy new (did my research of repairs). My new fridge tells me if I leave it open on accident which is amazing. Sure, it sounds stupid at first, but when you fill the freezer and something prevents closing, it is awesome to save things you worked or paid for.

I think I'm ready for the A+ certification now.

If that battery dies it's a pain in the ass especially in a custom built PC. All the BIOS settings will be reset as soon as the power is turned off. Luckily Asus BIOS allows you to save profiles which are non-volatile but it's still troublesome to load it every single time it boots.

Actually from what I understand not having a proper CMOS battery might mean your PC won't boot up at all, since if you have features not supported by the 'default settings' of the BIOS, your PC will be bricked. For example say you use SSD and your mobo was originally designed for IDE hard drives, and has to be set to support SSD because it's very old, stuff like that. So this Techquickie oversimplied things.

They didn’t always use a coin cell battery. Older computers used whatever they pleased, from +6V batteries, to AA, to the dreaded Dallas RTC chip with a built in battery that was often soldered in (requiring a replacement or DREMELING THE HOUSING TO ADD A COIN CELL BATTERY)

Complimentary : expressing a compliment; praising or approving. Complementary: combining in such a way as to enhance or emphasize the qualities of each other or another. Complementary metal-oxide-semiconductor (note the hyphens) is the correct form. BTW the Metal-Oxide-Semiconductor describes the 3 basic layers of the construction (originally Aluminium now polysilicon, Silicon dioxide , doped silicon), not some mythical Semiconductor that is a metal oxide.

I was wondering why my PC wasn't keeping track of time after it turns off then on again. If I turned it off at 8:24pm, next morning turing it on would keep it at 8:24pm until I manually have it connect to windows time server, despite it being set to automatic. I went through every setting I could find and checked the BIOS. Nothing. Until one of my friends reminded me about the CMOS battery. That was the problem. Although replacing it also reset the BIOS trying to find windows 10 uefi version instead of the one I had.

The clip of Linus pouring liquid nitrogen is everywhere.

LGR and other vintage computer YTers can certainly tell of the horror of ye olde Dallas real-time clock chips and soldered RTC batteries...

Hang on, "[NTP] isn't commonly used on home PCs", that doesn't sound right, I'm pretty sure every desktop OS (and every mobile OS for that matter) connects to NTP servers to get the correct time, the same way servers do. The battery just helps in case you're not connected to the internet when you boot up.

One time I changed the graphics output in my bios to the integrated gpu in my dell precision. ..but it had an intel xeon. If that little battery diddnt exist the system would have been bricked forever.

As an Electronics Engineer who works with digital semiconductor design. When someone starts talking to me about CMOS it throws me off every time that they’re just talking about a nvrm for bios. Like, most of the board is CMOS. lol

Basically, its a CMOS battery, which is needed for storing BIOS settings on motherboards. These batteries are not needed for your PC anymore for BIOS settings anymore, *BUT* they are needed for time settings on home computers.

Make sure to buy the battery from a store which have the latest manufacturer item as I bought this battery from a radom electronic store the battery had around 2.8v and my computer need 3.3v and that was frustrating to fix

Oohh. So that’s why I found batteries in my old Nintendo cartridges. Good save.

I have a vintage motherboard in storage that uses jumpers for settings instead of a BIOS menu system. It's got jumpers all over the motherboard with labels for each. Funky stuff.

Great video , one computer that comes to mind that does not have a RTC is the raspberry pi. The ironic thing is that I have a pi4 running Ubuntu as a local ntp server.

My laptop has a faculty battery. But since it connected via wires it quite a pain to replace. But since the laptop has another battery it's no problem, as long as I keep the laptop battery in the coin battery can be disconnected.

i know about this cmos batt but i never changed my cmos batt in my 2011 lenovo t420 still works and keeps time 100% correct

yeh, mines just got pins you touch with a paperclip I don't think any board makes you remove the battery anymore to reset it. but yeh, that works too.

I came across several Microsoft Surface devices that lost their clocks when they were powered off. They were old, so I suspected that their clock batteries had gone bad. We couldn't replace them, though.

While you imply they are not needed, servers in datacenters do have the same CR2032 coin cell battery on board. So do the network switches and chassis managers. You will spot them in hardware teardowns on ServeTheHome, and in Open Compute server documentation. I'm curious if anyone knows of exceptions - a server (not RPi or SBC) with no CR2032.

If I remember correctly my old gateway computer used to tell me when the battery needed replacement.

I have one that's over ten years old and it clears all my BIOS settings to default when the power is turned off. Guess I should change it.

Joke's on you motherboard; I keep track of my RAM timings with a spreadsheet.

We opened up the PS4 and we saw this installed in the Motherboard. ✌️ Had to replace one on my Truck Keys Remote Locker / Unlocker and the Motherboard. 😯

4:03 Yes, Roman, we feel your pain, now more than ever. 😂

old PCs used to use NiCd rechargeables - if you've got one somewhere cut out the battery as it will leak!

fun fact: If the CMOS in the ps4 dies or gets removed you can't play games on it anymore

I remember Amstrad PC1640 and PC 1520 used to use AA batteries on the top of the base under the monitor stand for the CMOS

The computers I have had over decades of which I typically keep for over 12 years have never had a battery issue. I am confused though about - if a computer is either left on 24/7 or mostly left in Sleep mode 99% of the time, does the regular power supply take over from the battery thus greatly extending it's life? I always wondered as to why a battery can last 12 years or more. Thanks

Lmao, that clip of Roman and Linus at the end

My PlayStation 2's cmos is still working and displaying the date correctly 18 years after I bought it, not sure if it's a miracle or what

I already know about the CMOS Battery, but I like these videos anyways!!!

I'm not sure if my battery is still working after 10 years, but I never replaced it in my MSI PH67 mobo. Still works like a champ

what in the... i literally was just looking at the CMOS battery of my motherboard, and thinking "why does it need that?" and few hours later, got this video recommended.

I had to replace that battery once when I bought a PC from Goodwill

I think one thing is really good about the video but first I want to thank MSI for the sponsorship

If every company in tech named their products like the battery industry it would be great. The code CR2032 the C means its lithium. The R means its round. The numbers stand for 20x32mm for the diameter. And whats with the knock off brandless Maxell knock off battery on the cover photo motherboard? Legit same batteries you find at the dollar store. Wouldnt trust it with the alarm on my watch let alone my computer

So question. When replacing the cmos battery, what is important? I know the size but how do I know what one to use?

The info about NTP is wrong! NTP is used by default on Windows, Android and almost all Linux distros. I haven't used any Apple products, but I'd be very surprised, if they don't use NTP. Also, NTP is not only used at boot time but also at regular intervals while the device is running.

I wish that removing the battery to clear cmos (bios settings) was an option that you could disable if you dont want that feature and want it to retain the settings.

Oh... so maybe this is why an old laptop our family owned would always have the wrong date and time whenever we turned it on: because the battery was probably dead.

I don't know if they use NTP or not, but Windows desktops do attempt to sync with time servers. If in a domain, it's the domain controller, if not then I think it defaults to a server at Microsoft. Linux desktops also come with NTP (though it may not always be enabled by default).

I don't know why home computers still need a cmos battery. Doesn't the clock automatically update when connected to the internet anyway on modern computers?

Why not use a capacitor like the original Xbox used (that is also now a source of corrosion, but that's more of an age and cheap component problem)? Tradition, but then remove the battery, put a cap and put a clear CMOS button? Idk. I'm just spit ballin ideas.

I'm curious how many of those tops Riley owns. They look so comfy.

My clear cmos jumper is under the gfx card for some reason, so the battery is always quicker.

This has to be the most common knowledge things in the computer space.

Why do some motherboards like laptop ones not have the cmos battery?

CMOS battery .... take it out and watch what happens lol 😆 Another interesting thing is that you can turn on a PSU without a motherboard, you just have to jump two pins on the 24pin connector to "trick" it.

I put my old CMOS Battery on my wrist watch and it works. Saves me a dime for a new battery

My Computer Tech class literally just covered this. I might as well start treating this channel as part of my course LOL

I know the "magic spell" joke probably wasn't a Dresden files reference But im gonna choose to believe that it was