BIOS date/time reset itself if power supply is cut off. What happened?

I have old Asus Notebook that I have not used for 1 year and more (but my dad & brother sometimes used it). The notebok battery has already broken so I detach it from the notebook. Thus the notebook only powered with cable power adapter.

Recently, I turned on the notebook and find out the BIOS date & time is reset to 01/01/2000 & 12:00:00. I also remember that I had set a password for the BIOS but now it's gone, all settings seems back to default.

Then I fixed the BIOS date/time. But interesting thing that I found if I restart or turn-off-then-turn-on the notebook without unplugging the power adapter, the BIOS date/time are not reset to default. But if I turn off the notebook, then unplug the power adapter and replug again, then turn on the notebook again, the BIOS date/time and settings will reset to default.

So what does happened to my notebook after all?
10 answers Last reply
More about bios date time reset power supply happened
  1. Because the bios battery is used to retain the settings of the Date and time RTC Real Time Clock. it always have to have power to it. that is why the battery is there to keep the time and date right. And retain all the current saved settings. Unplug the main power without a Cmos battery = Bios restet every time.
  2. weaselman said:
    Because the bios battery is used to retain the settings of the Date and time RTC Real Time Clock. it always have to have power to it. that is why the battery is there to keep the time and date right. And retain all the current saved settings.

    Isn't it cmos battery alone is enough to save the date/time setting? I only detach the notebook battery, so that means I only use power adapter to start the notebook. All this time, there is no problem of BIOS date/time resetting itself until recently.

    weaselman said:
    Unplug the main power without a Cmos battery = Bios restet every time.

    Did you mean my cmos battery is missing? I haven't checked it yet though.
  3. the CMOS battery is there but it is used/dead
  4. Emerald said:
    the CMOS battery is there but it is used/dead

    So that means I have to replace the CMOS battery?

    How average is the max. age of CMOS battery? I bought the notebook at 2005, so it's been about 7 years.

    Duh, I tried to diassemble the notebook, but it's hard.
  5. CMOS batterylife varies. I've had MBs with batteries that lasted 12 years. But 7 years sounds about average.
  6. Yep. Dead CMOS battery. Same thing happened with my old IBM ThinkPad T40 I bought in 2003. I believe the CMOS battery died in 2008 or 2009.
  7. Hi,

    Even after I replaced CMOS battery, the BIOS clock keeps reseting. What does this mean? Any solutions?
  8. Test the battery to make sure it's delivering 3 volts. I've bought new batteries (and tried to reuse old batteries) that didn't carry the proper charge.
  9. I had the same problem...Bought new battery but CMOS still resets the date etc.
    So...I tested the housing of the battery...It has a Negative spring plate at the bottom and two positive folds at the top that make contact with the battery...So i bent them slightly untill i could test the signal on the back of the + and - pins on the motherboard... and FIXED. So easy! Hope this helps someone!
    Just be careful not to break them when you bend them...they are fragile.
  10. maybe bios was damage
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