How long do CMOS batteries last in a PC?

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A CMOS battery, short for complementary metal-oxide-semiconductor, is a round, flat battery connected to a computer motherboard; it usually has a dedicated slot near the BIOS chip. This is usually a CR2032 coin cell battery and comes pre-installed. Its purpose is to provide backup power to critical functions and components, such as the CMOS RAM chip, even when the system is powered off. Primarily, it keeps the motherboard’s real-time clock running, but it also preserves important BIOS settings by powering volatile memory during low-power states. It’s a battery like any other, which means it will drain over time and will eventually need to be replaced. When can you expect this, and what else happens when it happens?

First, a CMOS battery inside a computer can last between two and ten years, sometimes longer. They are not rechargeable. However, when the computer is turned on, the circuit bypasses the battery so that it does not discharge, thereby extending its life cycle. This doesn’t mean that a battery can’t fail sooner, but most of the time, CMOS batteries last for years and years, so users never have to deal with them. All computers have a CMOS battery, including laptops and mini PCs.

If and when a CMOS battery dies, you can simply replace it by swapping it with the appropriate size. It’s easy to do, only takes a few minutes at most, and batteries are readily available at almost any hardware store or retailer. Again, the most common size is CR2032, but some computers may also use CR2016 or CR2025. When they fail, they can cause many headaches, such as preventing your computer from booting.

Believe it or not, when a CMOS battery starts to fail because it runs out of power or fails, it can cause many problems that you may not immediately recognize. In fact, there’s enough overlap that many of the telltale signs that your motherboard is failing may actually be coming from the battery itself. A CMOS battery failure can throw you out of sync or cause incorrect system times and dates, complete wipe of your BIOS and user settings, boot issues, and much more. Yes, if your computer won’t boot, it may be a dead CMOS battery and not one of the many other common errors that can also ruin a computer. A dead CMOS battery can even cause the system to misrecognize installed hardware, ultimately leading to performance issues. If you didn’t know better, you might mistake these hardware issues for a problem with software drivers or security certificates.

What’s interesting is how easy it is to overlook the CMOS battery as the main culprit when troubleshooting. This is probably because they normally last a very long time, but also because they are somewhat hidden on the motherboard. But if you’ve had your computer for more than three years, this is where you should look first if you’re experiencing related symptoms. Since a multi-pack of CR2032 batteries costs less than $10, this is an inexpensive and inexpensive solution if it turns out to be the source of the problem. If you ever buy a second-hand or second-hand PC, there are several things you should check to make sure it works, but it’s also a good idea to replace the CMOS battery before you go.