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BIOS battery query

Discussion in 'General Hardware' started by CurlyWhirly, 4 Feb 2006.

  1. CurlyWhirly

    Wise Guy

    Joined: 24 May 2003

    Posts: 1,429

    Location: UK

    I have a query to do with the BIOS battery.
    Would I be right in thinking that the battery only provides power for the BIOS settings (including the time) while the PC is off or does the battery also provide power while the PC is on?

    I am just wondering if, generally speaking, the battery lasts longer if you have your PC on for most of the day as mine normally is.

    I do realise that most PC's are upgraded before the BIOS battery ever goes flat but I'm just curious :rolleyes:
     
  2. Scream

    Mobster

    Joined: 18 Oct 2002

    Posts: 4,637

    Location: The Darkside

    The Battery keeps the BIOS settings set hence why you switch the computer off and on, the setting remain the same. Sometimes if a jumper swap didn't clear the CMOS, you would remove the battery.

    If a system was not used for a year or so, the Battery should still have power to keep the setting and the clock going. Its really the clock that would use the most power.

    A few minutes charge of the battery would last for a good while but like any other rechargable battery, its good to keep recharging it.
     
    Last edited: 4 Feb 2006
  3. CurlyWhirly

    Wise Guy

    Joined: 24 May 2003

    Posts: 1,429

    Location: UK

    So are you saying that when the PC is on that the motherboard is recharging the battery then?

    If so, I had no idea that this was the case as I just thought that the battery keeps using it's power reserves until it eventually gets too drained and has to be replaced.
    Interesting indeed!

    Thanks for replying BTW :)
     
  4. lordedmond

    Wise Guy

    Joined: 14 Jun 2004

    Posts: 1,573

    Location: Tilchestune

    IMHO they are not rechargeable batt. just normal large button cells life approx 5 years

    look in your manual and google the batt. no. to find out
     
  5. CurlyWhirly

    Wise Guy

    Joined: 24 May 2003

    Posts: 1,429

    Location: UK

    Thanks.

    It doesn't say in the manual and to be honest it isn't important enough to me to physically inspect the motherboard!

    Let's say for instance that the battery has a 5 year life, would it lose it's charge more quickly if the PC was only used occasionally as opposed to being in regular use?

    That's what I was trying to find out but I didn't word the question properly :o
     
  6. Jeff Crawly

    PermaBanned

    Joined: 26 Jan 2006

    Posts: 172

    CMOS batterys are not rechargable cells..... FACT

    'would it lose it's charge more quickly if the PC was only used occasionally as opposed to being in regular use?'

    Makes very little difference.

    Constantly flashing the BIOS and changing settings in the BIOS will run it down quicker as these functions draw more current from the CMOS battery
     
    Last edited: 4 Feb 2006
  7. CurlyWhirly

    Wise Guy

    Joined: 24 May 2003

    Posts: 1,429

    Location: UK

    Thanks.

    I now know that CMOS batteries are not rechargeable, so I assume that the BIOS settings are powered by the battery even when the PC is on then?

    Also would I be right in thinking that the PC would still boot even if the CMOS battery was flat?
    The clock time would obviously be wrong but what about the actual BIOS settings?
    Would they revert to default settings?
     
  8. CurlyWhirly

    Wise Guy

    Joined: 24 May 2003

    Posts: 1,429

    Location: UK

    Crikey, I go into the BIOS quite frequently to have a nose!
    I didn't know that it runs the battery down quicker! :eek:

    I am upgrading to a 64 bit PC within the next 12 months so it doesn't really matter to me but as I intend on selling this PC cheaply (as it's over 3 years old), I just wondered whether the PC would still be able to boot if the CMOS battery went flat, hence my query.
     
    Last edited: 4 Feb 2006
  9. lordedmond

    Wise Guy

    Joined: 14 Jun 2004

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    Location: Tilchestune

    if your worried they are not more than a fiver just replace it


    I have never had on go flat on me
     
  10. CurlyWhirly

    Wise Guy

    Joined: 24 May 2003

    Posts: 1,429

    Location: UK

    I wasn't that worried just curious as to whether the PC would still boot with a flat CMOS battery!
     
  11. Steves_pc

    Hitman

    Joined: 18 Oct 2002

    Posts: 706

    Location: Near a Sandbank in Norfolk

    Theyre usually a 3v lithium coin cell (CR2032) no need to be rechargeable as they last for a good 3-5 years.

    The pc would start up no problem but there may be stuff like cpu settings that would be set to the default minimum but should still boot into windows assuming the 1st hdd is the bootable one.
     
  12. CurlyWhirly

    Wise Guy

    Joined: 24 May 2003

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    Location: UK

    Thanks.
    That's all I needed to know.
     
  13. Scream

    Mobster

    Joined: 18 Oct 2002

    Posts: 4,637

    Location: The Darkside

    My mistake. I just assumed they were rechargable because of the number of years they keep going for. I have an old PC were the battery has been going strong now for just over 9 years.

    Wish they would make batteries like that for my TV remote.
     
  14. CurlyWhirly

    Wise Guy

    Joined: 24 May 2003

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    Location: UK

    I have just read this thread and also this post:

    I'm curious :o
    When your CMOS battery dies do you just lose the date and time settings or are other BIOS settings affected as well :confused:

    I thought that the BIOS settings were also affected.
     
  15. lumocolor

    PermaBanned

    Joined: 16 Mar 2006

    Posts: 103

    When the CMOS battery dies every BIOS setting will revert back too default. (The same it does when you clear CMOS)
    When you place the jumper on the clear CMOS pins all it's doing is shorting out the CMOS battery's + and - lines which then in turn obviously lose's all your NON default BIOS settings, the BIOS PIC chip can no longer hold these changes as it has no power.
     
  16. CurlyWhirly

    Wise Guy

    Joined: 24 May 2003

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    Location: UK

    Thanks lumocolor :)