The word CMOS is an acronym for “complementary metal oxide semiconductor”. The CMOS battery is a small, round battery that lets you store the day, time, and month on your computer. It allows you to shut your PC down for an extended period of time and still have the correct time and date in place when you use your PC again. More importantly, the CMOS battery stores the BIOS settings of your computer. The BIOS enables us to identify what hardware is on the system and what device drivers to use. When the CMOS battery is weak, the BIOS loses data and the computer can start to malfunction. Let’s take a look at a few signs of a CMOS battery failure.
Symptoms of a CMOS Battery Failure
- Your PC consistently has the incorrect date and time settings. Also, the date/time keep getting reset even after you fix them in the BIOS. This is the most common CMOS battery failure sign.
- Your PC occasionally turns off or doesn’t start.
- Hardware drivers stop working at random.
- You may start to get errors while booting that say something like “CMOS checksum error” or “CMOS read error“.
- You may see some weird hardware issues such as your computer not being able to locate the mouse, keyboard, or printer.
Replacing a CMOS battery
Luckily, replacing a CMOS battery isn’t too difficult. The key to replacing your CMOS battery is making sure you purchase the correct battery. You will need to open up your PC to get to the battery. Check your PC’s manual for the best way to do this. Generally, this is a pretty simple task. Important: Make sure you shutdown and then unplug the computer before opening it up.
Next, remove the CMOS battery from the motherboard. It will look like the picture at the top of this post and will be seated on your motherboard. If you are having trouble getting the battery out, you can carefully use a small flat head screwdriver or knife to help. After you have the battery, you can either write down all the information listed on the battery, or you can simply take the battery with you when looking to buy a new one. While at the store, try to find the closest possible match. Try to get a battery with the same voltage.
Alternatively, you can search Google or Amazon for the exact code on the CMOS battery. For example, in the picture below, the battery you are looking for is a “CR2032”. So, you can simply search Amazon or Google for “CR2032 CMOS Battery” and then order the battery you need. Luckily, CMOS batteries aren’t super expensive.
After you have purchased the battery, just snap it into your motherboard and you should be good to go. You will know right away if it worked based on the behavior of your date/time settings.
I agree, your specified first sign of CMOS battery failure is the most common issue. Thanks for sharing this very useful information.
I am having problems with my computer losing the time and date every time we have a power failure. Since I live in Maine and am in the country we have a lot of short power failures and then my computer becomes stupid until the ISP up dates the date. Your explaniation of what hapens when the CMOS battrty has failed or is failing is exactly what is happenong and I do have lots of 2032 batterys aound since it is uaed in a lot of my stuff, ie. bathroom scale, watch etc.etc.etc. HP went into a major program to try and tell me what was wrong and wanted money to tell what was wrong and how to fix it, I didn’t believe her and then found you. Why is the internet so difficule to give up simple info. Just want to sell stuff and earn a livins, I guess.