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T 23, how long memory without Cmos battery?

Discussion in 'IBM Thinkpad' started by Lars, Mar 28, 2007.

  1. Lars

    Lars Guest

    Hi group,

    A friend has had some problems with his Cmos battery, which I
    had fixed for him. So we decided to swap batteries for a week.

    I took mine out and went to see him. We swopped. When I came
    back home some 3 hours had passed. To my surprise, when I booted
    up, I did not need to set Time and date, and was not thrown into
    the Bios setup at all.

    I thought that any more than a few minutes of having the Cmos
    battery removed would have the Thinkpad forget those settings.

    The Thinkpad was obviously switched off. Its power brick was plugged
    in but the main battery removed.

    T 23.


    Lars
    Stockholm
    Lars, Mar 28, 2007
    #1
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  2. Lars

    Phil Sherman Guest

    The easiest test to do is to remove AC power from the system and then
    remove the battery. Wait 5-10 min then plug in the system and boot it
    up. If you get thrown into the BIOS; then the obvious conclusion is that
    there is a "trickle" circuit when AC is available that supplies the same
    power that the CMOS battery does.

    Phil Sherman


    Lars wrote:
    > Hi group,
    >
    > A friend has had some problems with his Cmos battery, which I
    > had fixed for him. So we decided to swap batteries for a week.
    >
    > I took mine out and went to see him. We swopped. When I came
    > back home some 3 hours had passed. To my surprise, when I booted
    > up, I did not need to set Time and date, and was not thrown into
    > the Bios setup at all.
    >
    > I thought that any more than a few minutes of having the Cmos
    > battery removed would have the Thinkpad forget those settings.
    >
    > The Thinkpad was obviously switched off. Its power brick was plugged
    > in but the main battery removed.
    >
    > T 23.
    >
    >
    > Lars
    > Stockholm
    Phil Sherman, Mar 28, 2007
    #2
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  3. Lars

    Ben Myers Guest

    Most computers, laptop or otherwise, have the trickle circuit to power the CMOS,
    thereby prolonging CMOS battery life... Ben Myers

    On Wed, 28 Mar 2007 17:40:49 -0400, Phil Sherman <> wrote:

    >The easiest test to do is to remove AC power from the system and then
    >remove the battery. Wait 5-10 min then plug in the system and boot it
    >up. If you get thrown into the BIOS; then the obvious conclusion is that
    >there is a "trickle" circuit when AC is available that supplies the same
    >power that the CMOS battery does.
    >
    >Phil Sherman
    >
    >
    >Lars wrote:
    >> Hi group,
    >>
    >> A friend has had some problems with his Cmos battery, which I
    >> had fixed for him. So we decided to swap batteries for a week.
    >>
    >> I took mine out and went to see him. We swopped. When I came
    >> back home some 3 hours had passed. To my surprise, when I booted
    >> up, I did not need to set Time and date, and was not thrown into
    >> the Bios setup at all.
    >>
    >> I thought that any more than a few minutes of having the Cmos
    >> battery removed would have the Thinkpad forget those settings.
    >>
    >> The Thinkpad was obviously switched off. Its power brick was plugged
    >> in but the main battery removed.
    >>
    >> T 23.
    >>
    >>
    >> Lars
    >> Stockholm
    Ben Myers, Mar 29, 2007
    #3
  4. Lars

    Larry Guest

    Another tip...

    After you have removed the Main Battery, A/C adapter and CMOS battery, hold
    down the power switch for 30 seconds.

    This will bleed off any left-over internal voltage that may be lying around
    in caps or whatever else.

    This is also how you reset the Power Manager on most ThinkPads (except you
    don't have to remove the CMOS) starting with the T20. If I remember
    correctly, the TP600 series may have had a pinhole near the power switch for
    this (I could be wrong. It's been a while since I saw a TP600 :))

    -Larry

    "Phil Sherman" <> wrote in message
    news:MGFOh.525$...
    > The easiest test to do is to remove AC power from the system and then
    > remove the battery. Wait 5-10 min then plug in the system and boot it up.
    > If you get thrown into the BIOS; then the obvious conclusion is that there
    > is a "trickle" circuit when AC is available that supplies the same power
    > that the CMOS battery does.
    >
    > Phil Sherman
    >
    >
    > Lars wrote:
    >> Hi group,
    >>
    >> A friend has had some problems with his Cmos battery, which I had fixed
    >> for him. So we decided to swap batteries for a week.
    >>
    >> I took mine out and went to see him. We swopped. When I came back home
    >> some 3 hours had passed. To my surprise, when I booted
    >> up, I did not need to set Time and date, and was not thrown into
    >> the Bios setup at all.
    >>
    >> I thought that any more than a few minutes of having the Cmos battery
    >> removed would have the Thinkpad forget those settings.
    >>
    >> The Thinkpad was obviously switched off. Its power brick was plugged
    >> in but the main battery removed.
    >>
    >> T 23.
    >>
    >>
    >> Lars
    >> Stockholm
    Larry, Mar 29, 2007
    #4
  5. Lars

    Lars Guest

    On Thu, 29 Mar 2007 11:47:35 -0400, "Larry" <> wrote:

    >After you have removed the Main Battery, A/C adapter and CMOS battery, hold
    >down the power switch for 30 seconds.


    Thanks guys. I did not need to hold down the power switch. Unplugging
    the main power and leaving it out for about ten minutes, with the Cmos
    battery out, brought me back to point zero. I never knew about that
    trickle thing.

    I had replaced my friends Cmos battery with a standard Panasonic 2025.
    I use some gooey stuff that is intended for repair of car rear window
    heating coils, as a glue. And then put a bit of electric tape around.
    I have done this quite a few times for Thinkpads. If it runs OK at
    first it usually works for months and years.

    His battery had gone quite dead in just a year! There was only 0.3 V
    in it now. I replaced it again and now it works fine.

    It is quite tricky to plug that battery back in in the T machines!

    >This is also how you reset the Power Manager on most ThinkPads (except you
    >don't have to remove the CMOS) starting with the T20. If I remember
    >correctly, the TP600 series may have had a pinhole near the power switch for
    >this (I could be wrong. It's been a while since I saw a TP600 :))


    It seems you are right. I have never needed to do that, but now on
    checking my 600's, one X and one E, I see they both have something
    in a hole near the power switch.

    Lovely machines, the 600's. I have several, and some of them I keep
    running for weeks on end. Never a problem with them!

    Lars
    Stockholm
    Lars, Mar 29, 2007
    #5
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