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A motherboard battery keeps its real-time clock running when the computer is unplugged and, depending on the board, helps retain firmware setup settings. It does not power the computer or store the BIOS/UEFI program itself.
What the motherboard battery actually does
The small battery supplies a tiny backup power domain on the motherboard, chiefly for the real-time clock (RTC). The RTC keeps track of the date and time while the computer is shut down and disconnected from external power. Many desktop boards use a 3-volt CR2032 coin cell, though the exact battery and arrangement vary by system. Intel describes the battery on its server boards as powering the RTC and maintaining BIOS settings.
On a desktop that is off but still plugged in, the motherboard may receive standby power from the power supply. When the PC is unplugged, the power strip is switched off, or the PSU is disconnected, the coin cell can keep the RTC running. The battery is not a substitute for the PSU or a laptop’s main battery, and it does not run the CPU, RAM, fans, drives, or graphics card.
Traditionally, the battery also supported a small area of battery-backed memory—often called CMOS—that held firmware setup values such as boot order and hardware configuration. Modern boards may store some or all setup data in nonvolatile memory instead, so the precise role varies. The RTC is generally the battery’s essential continuing job. Intel distinguishes the BIOS from the CMOS memory used for BIOS settings.
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RTC, settings, and firmware are not the same thing
- RTC: The low-power clock that keeps date and time.
- Firmware settings: Configuration choices made in BIOS/UEFI setup, some of which may be reset if the board loses backup power.
- BIOS/UEFI firmware: The startup software stored in persistent memory on the motherboard. The coin cell does not contain or normally erase that program.
Why it is called a CMOS or BIOS battery
“CMOS battery” is a longstanding, convenient name. Older PCs used battery-backed CMOS RAM for clock and setup data, and the label remained common as storage designs changed. People also call it the RTC battery, motherboard battery, or BIOS battery. “RTC battery” is often the most technically precise name today. Saying that the battery “stores the BIOS” is inaccurate: it supports the clock and, on some designs, settings—not the firmware code.
What kind of battery does a motherboard use?
Many desktop motherboards use a non-rechargeable, 3 V lithium CR2032. Intel specifies that type for its server boards, and Dell identifies it for its desktop systems. These are common examples, not a guarantee for every computer.
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- CHILD SAFETY: BITTER TASTE ON BOTH SIDES TO HELP KEEP CHILDREN SAFE—Duracell CR2032 features a bitter taste coating applied to BOTH SIDES of the battery to help deter accidental ingestion by young children.
- SUPERIOR LONGEVITY: Duracell Lasts Longer Than Energizer 3-In-1* | *Duracell 2032 size only. Based on ANSI Digital Household test vs. Energizer 2032 3-in-1.
- QUALITY ASSURANCE: Every Duracell lithium coin battery is manufactured to precise specifications and guaranteed against defects in material and workmanship. Trusted in medical devices and safety applications.
- FAMILY-SAFE PACKAGING: Duracell CR2032 batteries are sold in child-safe packaging—an additional layer of safety for households with young children.
Some laptops, compact PCs, and servers use a wrapped cell, a coin cell with a two-wire connector, a custom pack, or a soldered battery. Check the marking on the installed battery and the computer or motherboard service manual. Match the specified type, format, connector, and polarity. Do not assume a CR2025 or CR2016 is interchangeable with a CR2032, and do not put a rechargeable LIR2032 in a socket designed for a non-rechargeable CR2032. For system-specific guidance, see Lenovo’s instructions to use the specified or manufacturer-recommended battery.
Symptoms of a failing motherboard battery
| What you notice | What it may mean |
|---|---|
| Date and time reset after the PC has been unplugged | A weak battery is a strong possibility, though a poor contact or another RTC problem can also be responsible. |
| A startup message such as “CMOS battery low,” “RTC battery low,” or a checksum warning | The board may have detected lost or unreliable clock or setup data. |
| Boot order or other firmware settings revert after complete power loss | Battery-backed settings may have reset; the exact settings retained depend on the board. |
| The PC is completely lifeless | A dead coin cell is not the usual explanation. Check wall power, PSU, cables, and motherboard power connections first. |
| A new battery fails within days or weeks | Check the battery type, age, orientation, and holder. A faulty holder or board may be draining it. |
A dead battery does not normally delete personal files, Windows or Linux, applications, or the BIOS/UEFI firmware. It can cause startup confusion if settings such as boot order reset, and startup problems are possible, but they have many other causes. Intel notes that battery issues can sometimes contribute to boot failures; do not treat a no-boot symptom alone as proof the battery is bad.
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How long does the battery last?
There is no reliable single lifespan for every board. Battery age and storage, temperature, RTC design, and how much time the computer spends without external power all matter. Manufacturer estimates differ: Dell gives a general estimate of two to three years for its desktops, while Intel gives different guidance for different systems and power conditions—up to four years on one server-board example when connected to AC, and about 1.5 years below the maintenance threshold when unplugged. Intel’s consumer troubleshooting guidance describes lifetimes that may reach around a decade. These are model-specific estimates, not promises that can be applied to every computer.
Replace the battery when the clock or settings symptoms appear. Replacing it proactively can also make sense when returning an old system to service after it has spent years unplugged. Leaving a desktop connected to AC may supply standby power, but it does not make the battery last forever.
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How to replace a desktop motherboard battery
Use the computer or motherboard’s service manual first; access and retention clips differ. If the battery is wired or the machine is a laptop, do not follow the loose-coin-cell steps below without model-specific instructions.
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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →- Shut down and disconnect power. Unplug the AC cable and other power sources. Briefly press the power button after unplugging. Follow the manufacturer’s instructions for opening the case and use reasonable electrostatic-discharge precautions.
- Find and identify the battery. Locate the motherboard holder and read the battery marking. Photograph which side faces up before removing it.
- Remove it gently. Release the holder’s retaining clip without bending it. Avoid metal tools for prying; Dell specifically warns against using metal objects for this step.
- Fit the exact replacement. Match the type and orientation. In common desktop holders the side marked “+” faces up, but verify this on your board. Do not force the clip or short the cell.
- Close the case and reconnect power. Start the PC and enter BIOS/UEFI setup if prompted. Set the date and time, then check boot order and any custom settings you use—such as memory profiles, fan curves, virtualization, or storage mode.
- Save and verify. Save the settings, restart, then shut down and disconnect AC power for several minutes. Check that the clock and settings remain correct when you reconnect and start the PC.
Dell’s desktop battery guide covers disconnecting power and safe removal; Lenovo’s model-specific procedure also emphasizes correct installation and resetting date and time afterward. Dispose of the old cell according to local rules. A bare battery replacement is usually a small repair; a full electronics toolkit is generally unnecessary if the case can be opened with an ordinary screwdriver.
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Replacing the battery is not the same as clearing CMOS
Replacing the battery restores the backup power source. Clearing CMOS or RTC settings resets firmware configuration, usually to defaults. Updating BIOS/UEFI replaces firmware code. These are separate actions.
Removing the battery can reset settings on some boards, but the result and required wait vary. Many boards have a clear-CMOS button or jumper with a model-specific procedure; use the manual rather than guessing or leaving the battery out for a generic length of time. Intel describes jumper and clear-control approaches. A reset may help after unstable overclocking or an incorrect firmware change, but it can also mean re-entering desired settings. A clear-CMOS control does not replace the battery that keeps the RTC running.
What if the clock or settings still reset?
- Clock resets, otherwise normal: Confirm the battery type and orientation, replace it with a fresh cell, set time in BIOS/UEFI, and test after fully disconnecting AC.
- Settings reset every shutdown: Check for a clear-CMOS jumper left in the reset position and confirm that you saved changes before exiting setup. If a correctly installed fresh battery does not help, the holder, board, or power-management circuitry may be at fault.
- PC will not boot: Check power connections, RAM seating and memory training, graphics output, diagnostic LEDs or beep codes, and the manufacturer’s recovery procedure. A reset boot order can matter, but the battery is only one possible cause.
- Repeatedly short battery life: Verify that the replacement is fresh and the correct chemistry and format. If multiple correct cells die unusually quickly, suspect the holder or motherboard rather than assuming all coin cells are defective.
What about laptops?
A laptop may not have an exposed coin cell. Its RTC battery could be a wrapped pack with a connector, a soldered cell, or a model-specific design. Even where the voltage is similar, a loose CR2032 may not physically fit or connect safely. Find the exact model’s service manual and use its specified part and procedure; some repairs require board-level work. iFixit documents laptop examples where the RTC battery is soldered to the motherboard.
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