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how long does a cmos battery last

 Virtually all PCs both desktop and laptop have such a battery commonly referred to as a "CMOS" battery. This serves an important function although in fact most machines can be run without them, one which quickly becomes annoying.

The good news is that as you can see they usually last for years.

"CMOS" stands for "Complementary metal–oxide–semiconductor", the original technology that was originally used in some of the circuits that the battery was used to operate. 

While no longer the case the term "CMOS" or CMOS battery continues to live anyway.

The purpose of a CMOS battery today is simply to allow your computer to remember the time. I think of it as a glorified clock battery. If the battery is dead or removed then when the computer restarts it will forget the current date and time.

How Long Does BIOS Battery Last

Usually, the CMOS battery no longer affects the memory of the BIOS settings or not. Most of these settings are stored in a dedicated flash memory type, unlike the type that might be inside a USB flash drive

In the past when the battery actually activated the "CMOS RAM" to maintain these settings removing the CMOS battery will cause the loss of your BIOS to lose not only the date and time but also all the customizations you made on the BIOS configuration.

The reason you still need a battery is very simple: no matter what happens to the computer whether it is turned off or off the watch needs to keep running to keep track of the current time.

And this is by far the most common symptom: one day you boot your machine and it thinks it's January 1 1980 or some other random date in the past. It's time to replace the battery.

Apparently I never proactively replaced the battery. I'm just waiting for him to die and replacing him then. 

These batteries last so long that often the computer is not old and no longer in service anyway.

In desktops, the battery is usually relatively easy to replace. All you have to do after removing the power is open the case and see on the motherboard and it's probably there.

Laptop users have a harder time. Not only are laptops usually not designed for easy opening often the components are in hard-to-reach places. 

It is not uncommon to partially disassemble a laptop to get a CMOS battery. I had one case where I just let the battery die and did not replace it … it was too hard.

I avoided a lot of details because, to be honest, the details vary greatly from manufacturer to manufacturer and even from battery to battery. Some may last a year or two others a decade. 

Some BIOS will only lose time and others will lose more. Some machines are designed to facilitate battery replacement, others not so much.

Do not worry about it until your computer starts losing the current time and date on each boot. Then contact your computer manufacturer for instructions on how to replace a CMOS battery and which battery to replace.

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