# Can a CMOS battery die in a few months?



## Leoplate25 (Nov 21, 2019)

Hi, i have a little issue, and i assume it's the CMOS battery. It happens randomly. But whenever i shut the PC down and plug it off the wall (because here in Argentina we have horrible electriciy companies and for safety i plug off the PC from the wall) the CMOS battery resets the BIOS to its defaults, time get stuck at the time i shut the PC down for the last time, but it keeps the profiles i saved. I remove the battery and i saw some dust in it, but just now i replaced with another one. The question is: Can the CMOS battery die or fail in 9 months, or can it be that it was a little bit dirty in the underside? I have a Maximus Hero XI WiFi with an i5-9600k. Thanks in advance!


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## Grog6 (Nov 21, 2019)

Not normally, no.

To see if it's the battery causing the problem, measure the voltage of the battery with a voltmeter.

They won't hold anymore at ~2.0V, so if the battery measures this or below, it's bad.

I've pulled them from motherboards 10 years later, and they were still over 3V. (~3.3 is new, 3.7 is li ion chemistry, sorry.)

Those batteries only supply a few microamps of current; they don't really wear out, as much as age out after 5 to 10 years, when the battery material finally dies.

I've never personally had one die within ~10 years.

If there's a capacitor on that circuit, it may be shorting, and causing a problem, or dirt might cause a short, but it really should last 10 years.

If you think it's the motherboard, measure the current draw the motherboard is drawing from the battery with an ammeter. (a hand multimeter will not measure that current, so if it shows a current draw at all, something's bad.) It should be below ~5 microamps.

EDIT: I see you're unplugging from the wall; Modern computers use a bunch of standby current, up to 3A is the spec these days.
With everything having a settable operating point, like video cards and such, maybe it draws more current. IDK.

If your power is terrible, we used to use a SOLA transformer to clean up the power; they're pretty expensive, and run hot, so it may not be an option.






						Sola/Hevi-Duty Products | Sola Power Conditioning
					

Sola Hevi-Duty's ferroresonant power conditioners protect equipment from all power problems other than a complete loss of power. They excel at tightly regulating voltage within ±1.0% for input variations up to +10%/-20%, provide superior noise attenuation and are designed to withstand the...



					solahevidutysales.com
				





EDIT2:
Intel has something pertinent. This is old, too; modern boards may use even more power.









						CMOS Battery on Intel® Desktop Boards
					

Information on replacing the CMOS battery on Intel® Desktop Boards.




					www.intel.com
				






> A coin-cell battery (CR2032) powers the real-time clock and CMOS memory. *When the computer is not plugged into a wall socket, the battery has an estimated life of three years. When the computer is plugged in, the standby current from the power supply extends the life of the battery.* The clock is accurate to plus or minus 13 minutes/year at 25 degrees C with 3.3 VSB applied.



SO, yeah, it could possibly be a wear item.
If you change it with the power on, it should keep the settings, though.


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## Leoplate25 (Nov 21, 2019)

Grog6 said:


> Not normally, no.
> 
> To see if it's the battery causing the problem, measure the voltage of the battery with a voltmeter.
> 
> ...



I have low tension, i don't know the real translation, and a tension elevator (i don't know the real trasnlation either) to keep the electricity watts normalized. Now i remember i use to had a problem with a Z97 gigabyte motherboard, similar to this, and it was dirt in the battery. Thanks for your info btw.


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## Grog6 (Nov 21, 2019)

Tension translates to Voltage, I think, so if you have a tapped transformer, with the voltage raised, it makes the variations in voltage bigger.

I've seen that problem; it can make an old style TV go pow! 

Modern TV's have power supplies like computers, so not so much anymore.

Make sure the power supplies you buy are 110-240V rated, and it will minimize problems too.


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## Leoplate25 (Nov 21, 2019)

Grog6 said:


> Tension translates to Voltage, I think, so if you have a tapped transformer, with the voltage raised, it makes the variations in voltage bigger.
> 
> I've seen that problem; it can make an old style TV go pow!
> 
> ...


I have an UPS too. Here's is 220v and now i have 216v. The thing is when i had a GTX 1070 i didn't have the problem. The problem started when i bought a 2070. Can it be applying pressure to the CMOS battery. It just under the card or is it just coincidence?


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## newtekie1 (Nov 21, 2019)

Leoplate25 said:


> I have an UPS too. Here's is 220v and now i have 216v. The thing is when i had a GTX 1070 i didn't have the problem. The problem started when i bought a 2070. Can it be applying pressure to the CMOS battery. It just under the card or is it just coincidence?



The battery isn't rechargeable, so it's just going to slowly drain over time.  If you are asking it to power the CMOS for several hours every single day, I can definitely see it dying in less than a year.  I've put computers in storage for just a couple months, and come back to them with dead CMOS batteries.

And if you get a decent power supply with active PFC, you shouldn't need to unplug your computer, especially if you have an UPS.


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## Leoplate25 (Nov 21, 2019)

newtekie1 said:


> The battery isn't rechargeable, so it's just going to slowly drain over time.  If you are asking it to power the CMOS for several hours every single day, I can definitely see it dying in less than a year.  I've put computers in storage for just a couple months, and come back to them with dead CMOS batteries.
> 
> And if you get a decent power supply with active PFC, you shouldn't need to unplug your computer, especially if you have an UPS.


Thanks for your answer. I have a BitFenix Whisper M 750w.


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## newtekie1 (Nov 21, 2019)

Leoplate25 said:


> Thanks for your answer. I have a BitFenix Whisper M 750w.



You should be fine to leave it plugged in.  It will handle anything from 100 to 240v.  Plus, if you have it plugged into a UPS, the UPS should protect the computer.


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## Leoplate25 (Nov 21, 2019)

newtekie1 said:


> You should be fine to leave it plugged in.  It will handle anything from 100 to 240v.  Plus, if you have it plugged into a UPS, the UPS should protect the computer.


Thanks for your time! I'll do that.


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## Grog6 (Nov 21, 2019)

The video card probably draws some power to save settings as well, so it could be the source of the problem.

Leaving it plugged in should fix the issue; that way it draws off the VSB from the power supply.


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## Leoplate25 (Nov 21, 2019)

Grog6 said:


> The video card probably draws some power to save settings as well, so it could be the source of the problem.
> 
> Leaving it plugged in should fix the issue; that way it draws off the VSB from the power supply.


Thanks! One question: When the CMOS resets it reset everything on BIOS except for the profiles i saved. The time stucks at the hour i shut down and unplug the PC. Shouldn't the time be 00.00hs? Or am i wrong?


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## Grog6 (Nov 21, 2019)

The overclocking profiles on my mobo are saved in flash ram, apparently, because you have to overwrite them to change them; clearing CMOS won't lose them.

I think that's on purpose, so you wont have to reset everything if you have to recover from a bad OC. 
I've had to clear cmos to get it to boot before, lol.
Like the time it tried to boot at 5.1GHz, lol.


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## Leoplate25 (Nov 21, 2019)

Grog6 said:


> The overclocking profiles on my mobo are saved in flash ram, apparently, because you have to overwrite them to change them; clearing CMOS won't lose them.
> 
> I think that's on purpose, so you wont have to reset everything if you have to recover from a bad OC.
> I've had to clear cmos to get it to boot before, lol.
> Like the time it tried to boot at 5.1GHz, lol.


Well, thanks. I'll try keeping the PC plugged in and see what happens with the new CMOS battery. Have a nice day!


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## Grog6 (Nov 21, 2019)

If your battery is a 2016, you might see if you can get a 2020 or 2032 to fit in the holder; the difference is the thickness.

20xx is 20mm dia, and the xx16 is 1.6mm thick.

Typically, a 2032 lasts twice as long as a 2016.

Have a great day!


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## Leoplate25 (Nov 21, 2019)

Grog6 said:


> If your battery is a 2016, you might see if you can get a 2020 or 2032 to fit in the holder; the difference is the thickness.
> 
> 20xx is 20mm dia, and the xx16 is 1.6mm thick.
> 
> ...


I always use 2032. Thanks. Have a great day (again, haha).


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## jaggerwild (Nov 21, 2019)

Leoplate25 said:


> Hi, i have a little issue, and i assume it's the CMOS battery. It happens randomly. But whenever i shut the PC down and plug it off the wall (because here in Argentina we have horrible electriciy companies and for safety i plug off the PC from the wall) the CMOS battery resets the BIOS to its defaults, time get stuck at the time i shut the PC down for the last time, but it keeps the profiles i saved. I remove the battery and i saw some dust in it, but just now i replaced with another one. The question is: Can the CMOS battery die or fail in 9 months, or can it be that it was a little bit dirty in the underside? I have a Maximus Hero XI WiFi with an i5-9600k. Thanks in advance!



 A 3.3Volt battery will only save certain things, it will not save any settings such as an overclock. It will not keep current time as you unplug it(the wall plug does time) also internet does too. If you have dirty voltage you may consider a lap top, so it can be unplugged alot and still not have issue's such as your facing now.


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## R-T-B (Nov 21, 2019)

jaggerwild said:


> A 3.3Volt battery will only save certain things, it will not save any settings such as an overclock. It will not keep current time as you unplug it(the wall plug does time) also internet does too. If you have dirty voltage you may consider a lap top, so it can be unplugged alot and still not have issue's such as your facing now.



3.3 volt cmos battery absolutely will hold the rtc and mobo settings if unplugged, including and up to overclocking voltages and such.


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## Bill_Bright (Nov 21, 2019)

Leoplate25 said:
			
		

> The question is: Can the CMOS battery die or fail in 9 months, or can it be that it was a little bit dirty in the underside?


Of course they can die in that short of time! I've even had dead batteries right out of the brand new package! But normally they last years. 3 - 5 years is normal but I've even seen them last 8 - 10.

As for the battery being dirty, maybe. That depends on how dirty and what the dirt was.


> but just now i replaced with another one.


Good. But you may need to take it back out and clean it. When inserting these batteries, you should NEVER touch them with your bare fingers as skin oils promote corrosion and attract dust. So I always put a clean sock over my hand. If you touched the new battery with your bare fingers, it might need cleaning. And if the previous battery was dirty with grease/oil or other sticky contaminants, a good squirt with some quality electrical contact cleaner on the battery socket and contacts might be a good idea too.

Also, ALWAYS remember to unplug from the wall and touch bare metal of the case interior before reaching in to discharge any static in your body first.



R-T-B said:


> 3.3 volt cmos battery absolutely will hold the rtc and mobo settings if unplugged, including and up to overclocking voltages and such.


Except for them being 3.0V CR2032 batteries (not 3.3V - that's a PSU voltage), R-T-B is correct and the CMOS battery will indeed save OC settings. And one of its primary functions is to keep the RTC (real time clock) ticking when you unplug from the wall (or have a power outage). That's common knowledge so can only assume jaggerwild was tired and suffered from cranial flatulence when he said otherwise.

If you unplug from the wall (or flip the PSU master power switch to off) and your motherboard forgets the date & time (and boot order), the first thing you do is replace the CMOS battery.

And BTW, those lithium batteries should be recycled, not tossed in the trash. Here in the US, Best Buy will take them.


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## jsfitz54 (Nov 21, 2019)

Bill_Bright said:


> Of course they can die in that short of time! I've even had dead batteries right out of the brand new package! But normally they last years. 3 - 5 years is normal but I've even seen them last 8 - 10.
> 
> As for the battery being dirty, maybe. That depends on how dirty and what the dirt was.
> Good. But you may need to take it back out and clean it. When inserting these batteries, you should NEVER touch them with your bare fingers as skin oils promote corrosion and attract dust. So I always put a clean sock over my hand. If you touched the new battery with your bare fingers, it might need cleaning. And if the previous battery was dirty with grease/oil or other sticky contaminants, a good squirt with some quality electrical contact cleaner on the battery socket and contacts might be a good idea too.
> ...



@Bill_Bright :  You are correct in stating that the CR2032 is rated at 3V but a new fresh battery is always more than 3V so 3.3V is a fresh battery. Another example is a car 12V battery that should be at 12.6-12.7V and needs an alternator to charge at 14V ( a greater amount than the battery can hold, you can't charge at 12v.)

A third example is a AA battery when fresh should be 1.57v or thereabouts.

A stated rated battery voltage is the lowest its rated for.  They wear down from the over-volt and still remain in spec.


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## Bill_Bright (Nov 21, 2019)

jsfitz54 said:


> @Bill_Bright : You are correct in stating that the CR2032 is rated at 3V but a new fresh battery is always more than 3V so 3.3V is a fresh battery. Another example is a car 12V battery that should be at 12.6-12.7V and needs an alternator to charge at 14V ( a greater amount than the battery can hold, you can't charge at 12v.)


True but not the point or pertinent to this thread. Just because a fresh or fully charged battery (assuming in good working condition) holds more than the rated voltage, it is NOT rated at that higher voltage. 

A 12VDC car battery is still rated (and labeled) as a 12VDC car battery just as a CR2032 is rated and labeled as 3VDC and AA and AAA are rated and labeled as 1.5VDC (unless rechargeable - but that too is for another discussion).

Plus, in the case of that car battery, as soon as you remover the charger, the voltage will begin to drop and settle in around 12VDC. 


jsfitz54 said:


> you can't charge at 12v


Sure you can. You just will never get a "full" charge.

Also, as you noted, you are talking about fresh (new) or fully charged batteries. Batteries are only fresh, when fresh. So your points, while true, are really moot and irrelevant for the topic of this thread.


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## Grog6 (Nov 21, 2019)

The usual CMOS circuitry will hold info down to ~2.0V, some newer technology can go as low as ~1.6V, if the chip uses a 1.8V Vcc.

You need X number of diode drops to keep the internal circuitry biased properly; when it drops too low, it discharges the silicon capacitor thru the intrinsic diode inherent in how it's made.


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## jsfitz54 (Nov 21, 2019)

Bill_Bright said:


> *Sure you can.* You just will never get a "full" charge.



CAN but won't: Only some kind of idiot would kill the battery prematurely that way.


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## Grog6 (Nov 21, 2019)

Nomenclature is what you're referring to as a 3V or 12V battery.

The actual cell voltage is based on chemistry, a "12V" car battery, minimally charged is 2.2V/cell, or 13.2V.
They tend toward 2.25V cell if fully charged, or slightly higher, depending on Exact chemistry.

That's why the "Full charge" setting on cars is 14.4V, and the 'Float" level is 13.6Volts.
These voltages vary with temperature; that's why they recommend to do an equalizing charge on your car batter every three months or so.
Never heard of that? That's why you buy new batteries every few years, lol.
Battery manufacturers no longer provide info to keep your battery healthy; they want you buying new ones regularly.

If you measure 12V on a 12V car battery, you might be walking soon. 
That means it's heavily sulfated, if you are measuring it in your car.
And/Or your alternator is on it's way out.

For anyone interested, here's a good link. My car batteries last over 10 years, usually.





						Lead-based Batteries Information – Battery University
					

Learn about the differences within the lead acid battery family; the sealed lead acid (SLA), also known as gel cell, and the valve-regulated lead acid (VRLA).



					batteryuniversity.com
				





A Lithium primary battery at 3V is slightly discharged. It will decrease in the first few days to about 3v (2.9), and is considered dead at 2.7V, although for the purposes we're talking about here, there's a third of its life left.

If it doesn't measure at least 3.2V when you remove it from the package with a multimeter, it's an old battery.

Lithium Ion is 3.7V nominal, but will read 4.4V when removed from the charger, and is considered dead at 3V.
It's bad to let a li-ion battery totally discharge.

Back to the Topic: You can buy (or make) a CR123 Lithium primary battery with cables to plug onto the CMOS reset jumper, to override the battery on the motherboard; I haven't seen one in a while, but I know they exist. (Or used to)
That should last at least 10 years.

Make sure of the pinout of the reset jumper, it's usually "Battery, circuit, ground" but you want to be sure. 
When you reset, you're removing the jumper from the battery to circuit connection, and connecting the circuit to ground.
The override battery should be - to ground, + to circuit.


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## Bill_Bright (Nov 21, 2019)

jsfitz54 said:


> CAN but won't: Only some kind of idiot would kill the battery prematurely that way.


Huh? That will not kill a battery - especially a sealed lead-acid battery as used in cars since they do not suffer from memory effect. In fact, as long as the CCA rating is plenty big to turn the engine over on a cold day, there's no harm at all only charging the battery with an actual 12V charger. On a freezing cold morning, even a fully charged, brand new car battery will probably read below 12VDC anyway. After the car is started the alternator/charging system will top it off to ~14.2 to 14.6VDC.


Grog6 said:


> If you measure 12V on a 12V car battery, you might be walking soon.


Nah! Not true at all. With a perfectly good battery, let your car sit for a week and you will see it drops to 12V or even a bit below. Why? Because that battery is still keeping your vehicle's clock and computer and security system alive and will do so weeks. Even if totally disconnected, some chemical reactions are still going on. But it has to have enough reserve to still start the car - and that's not a problem.

If what you suggested was true, I sure would have been stranded at the airport a couple hundred times during my career as I used to take lots of 7 - 10 day business trips. Never had to get a jump.

Edit comment: Inserted left out "day" after 10.


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## Leoplate25 (Nov 21, 2019)

Thanks, guys, for all the answers. I learned a lot of things that i didn't know. Cheers!


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## Grog6 (Nov 21, 2019)

I had to work hard to learn what I know; I don't mind sharing at all. 
With Links and references, lol

Batteries all come down to their Amp-Hour capacity, all else is shapes and form factors. 

And with Lithium, Fire! 
Lol.


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## Bill_Bright (Nov 22, 2019)

Grog6 said:


> I had to work hard to learn what I know; I don't mind sharing at all.


Me too. And you can follow the link in my sig to see if I might know a little about electronics and how they work. And sharing what I know before those "little grey cells" decay away is why I come to forums like TPU. 

And for the record, no one disputed your links and references. The only thing you said that I disagreed with was the comment about walking soon if your 12V car battery measured 12V. 

BTW, if not a smoker, you might be interested in getting one of these for your vehicles. Very informative if your dash instrument panel only has an "idiot light" or does not include a gauge with actual numbers. It's a good suggestion for a stocking stuffer! 

And yes, with lithium batteries often comes fire - not to mention explosions too. But sadly, that is often due to poor (or no!) quality control at the factory or improper matching to the electronics it is supposed to support. And those are typically the result of putting profit over safety.


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## delshay (Nov 22, 2019)

I was thinking about doing an experiment & replace the battery with a coin type supercapacitor. Don't think it will be too hard to add-in the extra circuitry to charge the capacitor. This way I never need a battery. 

On my to do list.


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## Bill_Bright (Nov 22, 2019)

delshay said:


> This way I never need a battery.


Never? Ummm, that depends on how long the computer might go without power. The cap, regardless its capacity, will eventually discharge completely if given enough time. There are all sorts of scenarios where a computer may go without power for extended periods. You might go on an extended vacation and unplug before you go or severe weather may take out power to your whole neighborhood for 10 days or longer - just to name a couple. 

You wouldn't want the cap to be too big because you still may need to reset the BIOS by moving a jumper. You don't want sparks flying. 

Technically, using a cap instead of a battery would not be hard. And from a design, parts and operation cost point of view, is probably cheaper than using a battery socket and battery. And of course, capacitors are not the environmental hazard Li-Ion batteries are. But is it a good idea? I would say no. If it was, surely motherboard designers would have done it long ago just to save on production costs.


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## FordGT90Concept (Nov 23, 2019)

I had this problem with a MSI Neo 4 Platinum motherboard.  Contacted MSI about it, did an RMA, and the new board (newer revision) didn't have the problem.  Most likely there's a short circuit in the board that's causing excessive battery drain.  It's not normal (CMOS battery should last > 10 years) and it will always kill batteries until it's physically replaced with a revision or different board that doesn't put excessive load on the battery.


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## Space Lynx (Nov 23, 2019)

I ended up learning a lot from this thread, thanks OP... I always wondered about these little batteries lol


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## potato580+ (Nov 23, 2019)

no, evea fake one can worked well for years or so, ithink abt half quality of real product lifecyle, ive plenty on my office desk
sample of fake


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## Bill_Bright (Nov 23, 2019)

FordGT90Concept said:


> I had this problem with a MSI Neo 4 Platinum motherboard. Contacted MSI about it, did an RMA, and the new board (newer revision) didn't have the problem. Most likely there's a short circuit in the board that's causing excessive battery drain.
> 
> (CMOS battery should last > 10 years)


No doubt the new revision had nothing to do with this. The old board had a faulty component (it happens) that, as you noted, caused resistance in that circuit to drop, causing excessive battery drain. By perfect timing on your part, the RMA simply coincided with there being a new revision. Either way, kudos to MSI for taking care of you!  How a company takes care of their mistakes is one major factor in how we measure their reputation. If you didn't have to fight with them to get that RMA, then their reputation just rose a notch in my book! 

As far as CR2032 batteries lasting 10 years, that would really depend on the demands put on the battery during its life. PCs that are never (or rarely) unplugged, never have their master power switch set to off ("0") or in those countries where wall outlets are switched, never have that power switched off, those batteries will certainly have a longer useful life. 

But for PCs that, for most of their entire life span, are simply allowed to go into a standby state (which is any time the PSU is plugged into the wall, the master power switch remains set to on ("1"), and the wall outlet remains "live", the ATX Form Factor required +5Vsb standby voltage is still being delivered to the motherboard and that voltage, after being divided) is still used to keep the CMOS memory circuits, and the data contained within, alive without the help of the battery. No demands on the battery means a longer life.

But as newtekie1 correctly noted way back in post #6, the CR2032 batteries used on motherboards are not rechargeable. So if the motherboard goes through many periods of complete power outages, the battery will drain faster. So while 10+ years is certainly possible, 3 - 5 years is more the normal "expectancy". 

Also, not all batteries are created equal. My personal experience has shown me it is worth the extra money to make sure I buy CR2032 batteries with that pink bunny is on the label, and not some off-the-wall brand or no-name generics.


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## FordGT90Concept (Nov 23, 2019)

Bill_Bright said:


> By perfect timing on your part, the RMA simply coincided with there being a new revision. Either way, kudos to MSI for taking care of you!  How a company takes care of their mistakes is one major factor in how we measure their reputation. If you didn't have to fight with them to get that RMA, then their reputation just rose a notch in my book!


Bare in mind this was back in 2005.



Bill_Bright said:


> As far as CR2032 batteries lasting 10 years, that would really depend on the demands put on the battery during its life.


Had a Pentium II machine which sat unplugged for over a decade and never had the battery replaced.  It didn't lose its settings.  A well engineered motherboard should make the CMOS battery last at least as long as the board itself does.


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## Bill_Bright (Nov 23, 2019)

FordGT90Concept said:


> Bare in mind this was back in 2005.


Ah. Well things might have changed. Still Gigabyte treated me right back in the day when leaky electrolytic capacitors were wrecking havoc when they replaced a 4 year old mobo for free, 1 year after the 3-year warranty expired.  To this day, they are my preferred motherboard brand and I suspect will remain so (until they don't treat me right!). 



FordGT90Concept said:


> Had a Pentium II machine which sat unplugged for over a decade and never had the battery replaced. It didn't lose its settings. A well engineered motherboard should make the CMOS battery last at least as long as the board itself does.


I've seen them last that long too. But one or two examples do not make the rule. As I noted earlier, I've had brand new batteries that were bad straight out of the package. 

I do, however agree with and feel they should last as long as the board itself - which, IMO, should be at least until I retire it due to obsolescence - not because it died.


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## Grog6 (Nov 23, 2019)

delshay said:


> I was thinking about doing an experiment & replace the battery with a coin type supercapacitor. Don't think it will be too hard to add-in the extra circuitry to charge the capacitor. This way I never need a battery.
> 
> On my to do list.



There's problems with this.

The little battery stores more charge in its chemicals than a supercapacitor can hold, unless you're talking a big one. 

If there's a short, something goes Boom! loudly. 

Take this datasheet for example:



			http://www.vishay.com/docs/28409/196hvc.pdf
		


This is for a larger coin cell type, rated for 4.2V and 90Farads. 

According to the datasheet, it can supply 500uA for 24hours. 
(There's a table on Page 8.)
Assuming things are linear, (big assumption, but it should be for power delivered to a load) 500uA for 24 hours, 20uA would be 25 days.

If the load is larger, the time is proportionally shorter.

Also, if you look up the leakage value of the supercapacitor, you'll find it's higher than the load you're going to put on it, so it's lifetime is self defined, not load defined.
There's a table for this, as well, Page 10.
It says that after power has been on for 20 or so hours, the leakage current stabilizes at about 20uA, which is as much as the load we would expect.

To make a long story short, (too late!) the little battery is going to outperform any supercapacitor 50x its size.

If you really want to build a charging circuit to recharge something, look into the 18650 Li-ion cells; I have a bunch of those, and they last a LONG time with small loads.
A 5800mAh cell will keep your mobo alive for a year, at least. 

You can even buy a charging circuit cheap that would plug into a usb or molex power connector, that properly charges the cell.

A supercap story:
I worked with a tech that had the bright idea that he could replace his car battery with a huge supercap.  

The big limits on those are:

Temperature: Cars go to 180F+ easy under the hood; it's called "heat soak."
Charging: Supercaps will draw hundreds of amps charging off an alternator; that's not good for either part.
Discharging: Putting a starter motor across a capacitor is as close to a short as you will ever see. This was the "Nail in the Coffin", so to speak. 
When dude hit the starter after driving around the parking lot and parking again, and everything heated up to high temperature, the battery-sized supercapacitor exploded, ruining the hood, radiator, and some other stuff from shrapnel. 

So, be careful, and if you do decide to try using one, put the side of the case back on before you hit the power button, just to be safe.


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## Leoplate25 (Nov 24, 2019)

Keep learning stuff. Thanks, guys!


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## Cjake (Jun 2, 2020)

Hey had the same kind of problem with both my monitors just going blank along with my mouse and keyboard shutting off, I then changed the cmos battery out and it all works again but I checked my old battery and from what I've read its still good reading 3v. Any ideas on what could've caused this to happen?


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## Bones (Jun 2, 2020)

Cjake said:


> Hey had the same kind of problem with both my monitors just going blank along with my mouse and keyboard shutting off, I then changed the cmos battery out and it all works again but I checked my old battery and from what I've read its still good reading 3v. Any ideas on what could've caused this to happen?



Did you actually check the battery with a voltmeter to KNOW it still has 3.0v's?

Anything from below 2.9v's is bad enough to warrant changing it. 
It seems from what you describe the BIOS settings got scrambled somehow and by removing the battery you caused it to reset to defaults which corrected the problem you had. 
It's working again and that's the big thing here.


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