Nonvolatile BIOS memory

<h2 id="cmos-battery">CMOS battery</h2>

The memory battery (aka motherboard, CMOS, <a href="/facts/Real-time_clock/pYeXraUW">real-time clock</a> (RTC), clock battery)<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a><a class="footnote-ref" id="fnref:12" href="#fn:12">12</a> is generally a <a href="/facts/CR2032/fUaN3p0X">CR2032</a> <a href="/facts/Lithium_battery/D5yfo8XS">lithium</a> <a href="/facts/Coin_cell/fUaN3p0X">coin cell</a>. This cell battery has an estimated life of three years when <a href="/facts/Power_supply_unit_(computer)/3nvssXFG">power supply unit (PSU)</a> is unplugged or when the PSU power switch is turned off.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a> This battery type, unlike the <a href="/facts/Lithium-ion_battery/3L22xFhB">lithium-ion battery</a>, is not rechargeable and trying to do so may result in an explosion. Motherboards have circuitry preventing batteries from being charged and discharged when a motherboard is powered on. Other common battery cell types can last significantly longer or shorter periods, such as the smaller <a href="/facts/CR2016/fUaN3p0X">CR2016</a> which will generally last about 40% less time than CR2032. Higher temperatures and longer power-off time will shorten battery cell life. When replacing the battery cell, the system time and CMOS <a href="/facts/BIOS/AYYPUogS">BIOS</a> settings may revert to default values. Unwanted BIOS reset may be avoided by replacing the battery cell with the PSU power switch turned on and plugged into <a href="/facts/AC_power_plugs_and_sockets/938U5dTF">an electric wall socket</a>. On <a href="/facts/ATX/lzxcKxLF">ATX</a> motherboards, the PSU will supply 5V standby power to the motherboard to keep CMOS memory energized while the system is off.
Some computer designs have used non-button cell batteries, such as the cylindrical "<a href="/facts/List_of_battery_sizes/67MGwWxX">1/2 AA</a>" used in the <a href="/facts/Power_Mac_G4/VdKDJM1D">Power Mac G4</a> as well as some older <a href="/facts/IBM_PC_compatible/zGUpl7Sh">IBM PC compatibles</a>, or a 3-cell <a href="/facts/Nickel%E2%80%93cadmium_battery/JTbx4bcB">nickel–cadmium</a> (Ni–Cd) CMOS battery that looks like a "<a href="/facts/Barrel/ESCAffFw">barrel</a>" (common in <a href="/facts/Amiga/60B3A9of">Amiga</a> and older IBM PC compatibles), which serves the same purpose. These motherboards often have a four pin straight header, with pin 2 missing, for connecting to an external 3.6v battery, such as the Tadiran TL-5242/W, when their soldered-on batteries run out. Ni–Cd batteries have a tendency to <a href="/facts/Battery_leakage/JTYULFhf">leak devastatingly</a> after a period of disuse, damaging components and traces on the circuit board near the battery.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a>

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Extended_System_Configuration_Data/FCUk2TDm">Extended System Configuration Data</a> (ESCD)</li>
<li><a href="/facts/List_of_battery_types/xhL4zfRu">List of battery types</a></li></ul>

<h2 id="external-links">External links</h2>
<ul><li><a href="https://www.lifewire.com/what-is-cmos-2625826">Definition of CMOS & CMOS Batteries</a></li>
<li><a href="https://bochs.sourceforge.io/techspec/CMOS-reference.txt">CMOS memory map (for Bochs PC emulator)</a></li>
<li><a href="https://www.youtube.com/watch?v=0q2RIaCICKU">How to replace dead CMOS battery and configure BIOS settings</a> (video).</li>
<li><a href="https://www.youtube.com/watch?v=MTg8qhWKNpA">Tutorial: How to replace the CMOS battery in your laptop</a></li>
<li><a href="http://www.computerhope.com/issues/ch000239.htm">How to replace the CMOS battery</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Mueller, Scott (2004). Upgrading and Repairing PCS. Que. ISBN 978-0-7897-2974-3. <a href="978-0-7897-2974-3" target="_blank">978-0-7897-2974-3</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">Fisher, Tim. "What is CMOS? (CMOS & CMOS Battery Definition)". About.com. Archived from the original on 9 August 2016. Retrieved 2 September 2015. <a href="https://web.archive.org/web/20160809082556/http://pcsupport.about.com/od/termsc/g/cmos.htm" target="_blank">https://web.archive.org/web/20160809082556/http://pcsupport.about.com/od/termsc/g/cmos.htm</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Mueller, Scott (2003). Upgrading and Repairing PCS. Que. ISBN 978-0-7897-2745-9. <a href="978-0-7897-2745-9" target="_blank">978-0-7897-2745-9</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">"Intel 100 Series Chipset Family PCH Datasheet". Intel. August 2015. Retrieved 16 April 2016. <a href="http://www.intel.com/content/www/us/en/chipsets/100-series-chipset-datasheet-vol-1.html" target="_blank">http://www.intel.com/content/www/us/en/chipsets/100-series-chipset-datasheet-vol-1.html</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">"82430FX PCISET Data Sheet" (PDF). Intel. Retrieved 23 January 2023. <a href="https://www.intel.com/Assets/PDF/datasheet/290562.pdf" target="_blank">https://www.intel.com/Assets/PDF/datasheet/290562.pdf</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Mueller, Scott (2004). Upgrading and Repairing PCS. Que. ISBN 978-0-7897-2974-3. <a href="978-0-7897-2974-3" target="_blank">978-0-7897-2974-3</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">"Intel 100 Series Chipset Family PCH Datasheet". Intel. August 2015. Retrieved 16 April 2016. <a href="http://www.intel.com/content/www/us/en/chipsets/100-series-chipset-datasheet-vol-1.html" target="_blank">http://www.intel.com/content/www/us/en/chipsets/100-series-chipset-datasheet-vol-1.html</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">http://rom.by/files/AMIBIOS8-Flash-Recovery-Whitepaper.pdf [bare URL PDF] <a href="http://rom.by/files/AMIBIOS8-Flash-Recovery-Whitepaper.pdf" target="_blank">http://rom.by/files/AMIBIOS8-Flash-Recovery-Whitepaper.pdf</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">"UEFI NVRAM - OSDev Wiki". wiki.osdev.org. Retrieved 11 September 2020. <a href="https://wiki.osdev.org/UEFI_NVRAM" target="_blank">https://wiki.osdev.org/UEFI_NVRAM</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Yao, Jiewen; Zimmer, Vincent (2020). "Firmware Resiliency: Detection". Building Secure Firmware. pp. 115–162. doi:10.1007/978-1-4842-6106-4_4. ISBN 978-1-4842-6105-7. S2CID 242541772. <a href="978-1-4842-6105-7" target="_blank">978-1-4842-6105-7</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">Fisher, Tim. "What is CMOS? (CMOS & CMOS Battery Definition)". About.com. Archived from the original on 9 August 2016. Retrieved 2 September 2015. <a href="https://web.archive.org/web/20160809082556/http://pcsupport.about.com/od/termsc/g/cmos.htm" target="_blank">https://web.archive.org/web/20160809082556/http://pcsupport.about.com/od/termsc/g/cmos.htm</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Ask a question » Replacing the battery of your motherboard (CMOS battery) <a href="http://en.kioskea.net/faq/625-replacing-the-battery-of-your-motherboard-cmos-battery" target="_blank">http://en.kioskea.net/faq/625-replacing-the-battery-of-your-motherboard-cmos-battery</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">"CMOS Battery on the Intel NUC". Intel. 24 August 2020.
 <a href="http://www.intel.com/content/www/us/en/support/boards-and-kits/000006787.html" target="_blank">http://www.intel.com/content/www/us/en/support/boards-and-kits/000006787.html</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">Williams, Al (July 8, 2018). "Amiga 2000 Emergency Repair". Hackaday. Archived from the original on July 8, 2018. <a href="https://web.archive.org/web/20180708201017/https://hackaday.com/2018/07/08/amiga-2000-emergency-repair/" target="_blank">https://web.archive.org/web/20180708201017/https://hackaday.com/2018/07/08/amiga-2000-emergency-repair/</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
</ol>

Nonvolatile BIOS memory open-in-new

Nonvolatile BIOS memory