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    #1

    Capacitors instead of RTC/CMOS batteries

    Hi, would there be somekind of knowledgebase for laptops, that are using capacitors (+laptop battery) instead of RTC/CMOS batteries for keeping BIOS/UEFI values "alive/stored"?

    I learned hp and lenovo are doing this on their newer models a lot. I myself have a 2016 ASUS X540L here, that has not RTC/BIOS battery.

    Id like to know what to look for on the mainboards.
    Thank you in advance.
    Tags: None
  • Answer selected by STKR123 at 08-30-2024, 10:55 AM.
    bios settings are in flash,
    the rtc is built into the bridge chip and probably powered by a lithium rechargeable battery soldered to the board.
    super-capacitors as they are called are shit - companies tried them and mostly dropped the idea.
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      #2
      bios settings are in flash,
      the rtc is built into the bridge chip and probably powered by a lithium rechargeable battery soldered to the board.
      super-capacitors as they are called are shit - companies tried them and mostly dropped the idea.
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        #3
        Ah, "super capacitor".
        Now I found some more things to consider and to read.

        https://www.badcaps.net/forum/genera...uper-capacitor

        Thank you!

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          #4
          Stj just said it. While I do have some success with large super capacitors, the small one are a pain in the rear. If you want you can read my Fluke 289:super capacitor thread. That is one device for example where the manufacturer went from super caps to battery.

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            #5
            Super caps are good when they need to provide power for a short time [seconds, maybe minutes], such as in a dash cam after the ignition is turned off.

            They need to power it long enough to close files and do an orderly shutdown -- which shouldn't take more than a couple of seconds. Unlike batteries, their capacity won't change much, so they're a better option in that particular use.

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              #6
              they leak - they have no safe use

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                #7
                The original Xbox used a supercap. It was a 2.5v 1F cap and they are prone to failure. As long as the xbox was connected to mains, it would keep the cap charged and maintain the date/time. They expected that this would be the case as most people just leave their consoles plugged in all the time. In the event it was unplugged or there was a power failure, the cap would last a few hours or so before completely discharging.

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                  #8
                  Originally posted by stj View Post
                  they leak - they have no safe use
                  Evidence please showing that this is a widespread issue.

                  Comment

                    #9
                    Originally posted by aurgathor View Post

                    Evidence please showing that this is a widespread issue.
                    That's true for the small supercaps. The big ones do not have that leaking problem. I am running an experiment using large supercaps (two 25F in series) and with a solar panel and some device for 8 years now and all is good. The small supercaps just keep looking at the fluke 289 thread.

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