How Long to Leave CMOS Battery Out (2026 Complete Guide)
If you need to reset your BIOS settings to default, one of the most common methods is to remove the CMOS battery from your motherboard. But how long should you leave the CMOS battery out to ensure a complete reset? The answer is simpler than you might think, but there are important details about the process that can mean the difference between a successful reset and a frustrating experience. In this comprehensive 2026 guide, we will explain exactly how long to leave the CMOS battery out, why it works, what happens during the process, and alternative methods for resetting your BIOS without removing the battery at all.
Last updated: July 19, 2026 — Estimated reading time: 11 minutes
Table of Contents
- The Short Answer
- What Is the CMOS Battery and What Does It Do?
- Why Remove the CMOS Battery?
- How Long to Leave the CMOS Battery Out
- Step-by-Step Removal Process
- Alternative BIOS Reset Methods
- Using the Clear CMOS Jumper
- What Gets Reset and What Does Not
- What to Do After the Reset
- Frequently Asked Questions
The Short Answer
You should leave the CMOS battery out for at least 5 to 10 minutes to ensure a complete BIOS reset. This time allows the capacitors on the motherboard to fully discharge, clearing the CMOS memory that stores your BIOS settings. While some motherboards may clear with as little as 1 to 2 minutes without the battery, waiting 5 to 10 minutes provides a reliable margin that accounts for variations in capacitor quality and residual charge.
In most cases, leaving the battery out for about 5 minutes is sufficient. However, if you are dealing with stubborn BIOS settings that refuse to reset, or if your motherboard has particularly large capacitors in the CMOS circuit, waiting 15 to 30 minutes provides extra assurance. You do not need to leave the battery out for hours or overnight — the CMOS memory clears relatively quickly once the power source is removed.
The reason time matters is that the CMOS memory needs all stored charge to dissipate before it is fully cleared. The capacitors on the motherboard that support the CMOS circuit hold a small amount of charge even after the battery is removed. This charge gradually bleeds away through the resistive paths on the motherboard, but it takes a few minutes to fully drain. The exact time depends on the specific motherboard design and the components used.
What Is the CMOS Battery and What Does It Do?
CMOS stands for Complementary Metal-Oxide-Semiconductor, which is the type of memory chip used to store your BIOS or UEFI settings. This memory requires a small amount of constant power to retain its data, and the CMOS battery provides this power when the computer is turned off.
The CMOS battery is a small, coin-cell battery, typically a CR2032, mounted on the motherboard. It provides approximately 3 volts of power to the CMOS chip, which stores settings like the system date and time, boot order, overclocking configurations, security passwords, and hardware initialization parameters.
When the computer is powered on, the CMOS chip receives power from the power supply unit. When the computer is turned off, the CMOS battery takes over and maintains the stored settings. This is why your computer remembers the date, time, and BIOS settings even after being unplugged for extended periods.
The CMOS battery typically lasts 3 to 5 years in a desktop PC and 2 to 4 years in a laptop, depending on usage patterns and environmental conditions. When the battery dies, you may notice the system losing its date and time settings, resetting to default BIOS settings on every boot, or failing to POST (power-on self-test) correctly.
Why Remove the CMOS Battery?
There are several common reasons for removing the CMOS battery from a motherboard.
The most common reason is to reset the BIOS settings to their factory defaults. If you have made changes to BIOS settings that have caused instability, boot failures, or other problems, removing the CMOS battery clears all stored settings and restores the default configuration. This is often the first troubleshooting step when a computer fails to boot after BIOS changes.
Another reason is to clear a forgotten BIOS or power-on password. Some motherboards store the BIOS password in CMOS memory, and removing the battery clears the password along with all other settings. This can be useful if you have inherited a computer with a password you do not know, though some enterprise systems use alternative password storage methods that are not affected by CMOS battery removal.
CMOS battery removal is also used to resolve specific hardware detection issues. Sometimes the BIOS stores information about hardware configurations that conflicts with new hardware. Clearing the CMOS forces the BIOS to redetect all hardware on the next boot, which can resolve these conflicts.
Finally, when replacing a dead CMOS battery, removing the old battery before inserting the new one is a good practice that ensures a clean power cycle for the CMOS chip.
How Long to Leave the CMOS Battery Out
The time required to fully clear the CMOS memory depends on several factors, but here are the general guidelines.
For most modern motherboards, leaving the CMOS battery out for 5 minutes is sufficient to clear all settings. Modern motherboards use relatively small capacitors in the CMOS circuit, which discharge quickly once the battery is removed. Five minutes provides a comfortable margin beyond the minimum time needed.
If your motherboard is older or has been particularly stubborn about resetting, extending the time to 10 or 15 minutes provides additional assurance. Some older motherboards with larger capacitors may retain charge longer, and the extra time ensures a complete discharge.
For the most thorough reset, 30 minutes is more than enough for any motherboard. There is no benefit to leaving the battery out longer than 30 minutes, as the CMOS memory will have fully cleared long before that point.
A common mistake is leaving the battery out for only 30 seconds to 1 minute. This is often not enough time for the capacitors to fully discharge, especially if the motherboard was recently powered on. The residual charge in the capacitors may keep the CMOS memory alive long enough to preserve the settings, resulting in a failed reset.
Step-by-Step Removal Process
Follow these steps to safely remove and reinstall the CMOS battery for a BIOS reset.
First, shut down your computer completely and disconnect the power cord from the back of the power supply. If you are working on a laptop, also remove the laptop battery if it is accessible. This ensures there is no power source feeding the motherboard.
Press and hold the power button for 10 to 15 seconds. This drains any residual charge stored in the motherboard capacitors, which helps ensure a complete CMOS clear.
Open your computer case and locate the CMOS battery on the motherboard. It is a small, silver coin-cell battery, usually about the size of a nickel, sitting in a holder on the motherboard. It is typically located near the PCI Express slots or near the southbridge chipset, but the exact location varies by motherboard model.
Remove the CMOS battery by pressing the small metal tab on the side of the battery holder. The battery should pop up, and you can then lift it out with your fingers. Some battery holders have a sliding mechanism instead of a push tab. Be gentle and avoid using metal tools that could short-circuit nearby components.
Wait at least 5 minutes (10 to 15 minutes for extra assurance) with the battery removed and the power cord disconnected. During this time, the capacitors on the motherboard will discharge and the CMOS memory will be cleared.
Reinstall the CMOS battery by pressing it firmly into the holder until it clicks into place. Make sure the battery is oriented correctly, with the positive (+) side facing up.
Reconnect the power cord and power on your computer. The system should boot with default BIOS settings. You will likely see a message on the screen indicating that the BIOS has been reset and prompting you to enter setup to configure settings.
Alternative BIOS Reset Methods
If removing the CMOS battery seems too involved, there are several alternative methods for resetting your BIOS settings without physically removing the battery.
Many modern motherboards include a Clear CMOS jumper on the motherboard. This is a small set of two or three pins that, when bridged with a jumper cap, shorts the CMOS memory and clears the settings. To use this method, you locate the Clear CMOS jumper, move the jumper cap from its normal position to the clear position, wait a few seconds, then move it back. This achieves the same result as removing the battery but is faster and does not require battery removal.
Some motherboards have a Clear CMOS button on the rear I/O panel. This button performs the same function as the jumper — pressing it shorts the CMOS memory and clears the settings. This is the most convenient method when available, as you do not need to open the case at all.
For more details on motherboard troubleshooting, see our guide on how to jumpstart a motherboard. If you want to reset BIOS without removing the battery, check our article on how to reset BIOS without removing CMOS battery.
Some BIOS interfaces also allow you to load default settings from within the BIOS setup menu. If you can still access the BIOS, this is the simplest method — navigate to the “Load Optimized Defaults” or “Load Setup Defaults” option, save, and exit. This resets all settings without any physical intervention.
Using the Clear CMOS Jumper
The Clear CMOS jumper is the most common alternative to battery removal for resetting BIOS settings. Here is how to use it.
Locate the Clear CMOS jumper on your motherboard. It is typically labeled CLR_CMOS, CLEAR, JBT1, or similar, and consists of two or three pins. Check your motherboard manual for the exact location and pin configuration.
In the normal operating position, the jumper cap bridges two of the three pins (on 3-pin jumpers) or is absent (on 2-pin jumpers). To clear the CMOS, you move the jumper cap to the clear position, which bridges different pins. On 3-pin jumpers, you typically move the cap from pins 1-2 to pins 2-3. On 2-pin jumpers, you briefly bridge the two pins with a jumper cap or a screwdriver.
With the power cord disconnected, move the jumper to the clear position and wait 10 to 30 seconds. This is usually sufficient because the jumper creates a direct short that drains the CMOS capacitors much faster than simply removing the battery.
Move the jumper back to its normal operating position. Make sure you return it to the correct position, as leaving it in the clear position will prevent the CMOS from retaining any settings, causing the BIOS to reset on every boot.
Reconnect the power cord and boot the system. The BIOS should be reset to factory defaults.
What Gets Reset and What Does Not
When you clear the CMOS, not everything on the motherboard is affected. Understanding what gets reset and what does not helps set expectations for the process.
The following settings are cleared when you reset the CMOS: BIOS/UEFI settings and configuration, boot order and boot priority, overclocking settings and XMP/EXPO profiles, system date and time, BIOS passwords, hardware initialization parameters, and any custom fan curves or power management settings stored in the BIOS.
The following are NOT affected by a CMOS reset: the BIOS firmware itself (it remains unchanged), the operating system on your storage drives, files and data on your hard drives or SSDs, driver installations in your operating system, network configurations within the OS, and any settings stored in the operating system rather than the BIOS.
After a CMOS reset, you will typically need to reconfigure several settings in the BIOS before your system operates optimally. At minimum, you should set the correct date and time, configure the boot order to boot from your operating system drive, enable XMP or EXPO for your RAM if applicable, and adjust any custom settings you had previously configured.
For information on enabling performance features after a reset, see our guide on how to turn on PBO for AMD systems.
What to Do After the Reset
After successfully resetting your CMOS, there are several important steps to take before using your computer normally.
First, enter the BIOS setup by pressing the appropriate key during boot (usually Delete, F2, or F10, depending on your motherboard). The exact key is displayed briefly on the screen during the POST sequence.
Set the correct date and time. The CMOS reset will have reverted these to their default values, which may be significantly wrong. Incorrect date and time can cause issues with software activation, SSL certificates for web browsing, and scheduled tasks.
Configure the boot order to ensure your system boots from the correct drive. If you have multiple storage devices, make sure the drive containing your operating system is set as the first boot device.
If your RAM supports XMP (Intel) or EXPO (AMD) profiles for higher speeds, re-enable these settings. By default, RAM runs at its base speed after a CMOS reset, which is often slower than its rated speed. Enabling XMP or EXPO allows the RAM to run at its full rated speed.
Check any other settings you had previously customized, such as fan curves, power management options, virtualization settings, or security features. Re-apply your preferred configurations.
Save your changes and exit the BIOS. Your system should now boot into your operating system with the reset BIOS settings and your new customizations in place.
Frequently Asked Questions
How long should I leave the CMOS battery out for a full reset?
For most motherboards, 5 minutes is sufficient. For extra assurance, especially on older boards, leave it out for 10 to 15 minutes. There is no need to leave it out for hours — the CMOS memory clears within minutes once power is removed.
Will removing the CMOS battery delete my files?
No, removing the CMOS battery only clears BIOS/UEFI settings stored in the CMOS chip. It does not affect your hard drive, SSD, or any files stored on them. Your operating system, applications, and personal files remain completely untouched.
Can I reset the CMOS without removing the battery?
Yes, many motherboards have a Clear CMOS jumper or a Clear CMOS button on the rear I/O panel that achieves the same result without battery removal. Some BIOS interfaces also allow you to load default settings from within the setup menu.
What if my computer still has problems after a CMOS reset?
If problems persist after a CMOS reset, the issue is likely not related to BIOS settings. Consider checking hardware components, running memory diagnostics, testing your storage drives, or consulting a technician for further troubleshooting.
How do I know if my CMOS battery needs replacing?
Common signs include the system losing its date and time settings after being powered off, BIOS settings reverting to defaults on every boot, the system failing to detect hardware correctly, or error messages about CMOS checksum errors during POST.
Is it safe to remove the CMOS battery while the computer is plugged in?
No, always disconnect the power cord before removing the CMOS battery. Working on a powered motherboard risks electrical damage to components and personal injury. Follow proper ESD (electrostatic discharge) precautions as well.
What type of battery do most motherboards use?
The vast majority of desktop motherboards use a CR2032 lithium coin cell battery. This is a common, inexpensive battery available at most electronics stores. Some older or specialized motherboards may use different battery types, so check your motherboard manual to confirm.
Will a CMOS reset affect my Windows activation?
In most cases, no. Windows activation is tied to your Microsoft account and hardware fingerprint, not to BIOS settings. However, if your activation was based on a digital license tied to specific BIOS settings, a CMOS reset should not affect it because the BIOS firmware itself is not changed — only the settings within it are reset.
