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How to prolong life expectancy of CMOS coin cell abttery


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How to prolong life expectancy of CMOS coin cell abttery

  • Hi there,
    I recently read an article saying that for laptops or computers in general, if you leave the power plug connected to the electrical outlet even with the computer totally turned off, it will prevent the CMOS coin cell battery from being used up and its life expectancy will be prolonged. I have a laptop, and I use the AC adapter as my main power source for the most part. I connect my AC adapter to the surge protector unit which has a on/off button.

    My question is this: With my laptop turned off and the battery removed from the laptop, do I need to have the surge protector unit on or off to enable the AC adapter to receive some of the trickle electricity to prolong the life of the CMOS battery. I've noticed that when the surge protector is turned off, the AC adapter has a green light on the brick. Also, if I leave the AC adapter connected to the surge protector at all times (ie: when the laptop is turned on and then off), it starts making a high pitched sound after a long period of time. Surely this is not good for the AC adapter?

    Thank you for your advice on this matter.
  • Calla,

    I would leave your surge protector power strip on to keep power supplied to your Laptop and CMOS Cell.

    I reside in South Florida, within the corridor of the greatest frequency of Thunderstorm (and Lighting Strike) activity in the country and probably the world. There is a "surge-protector' at the house Main Power Junction Circut Breaker Box and I know of no Lighting related appliance damage in the past thirty years.

    Likely the greatest danger of Lightning Surge damage to your Computer would be through a Telephone/DSL or Cable line. I have a "Surge Protection" Power Strip which also takes the Telephone line in/out.

    Since this also powers the printer and other items, it is never turned off, the green light of the Dell Power Supply, would be dark if it were off. I have four Dell Power Supplies and have never heard any high pitched sound, but others have mentioned it in here.

    My first Portable was an IBM '386' rarely connected to Power Supply and within three years or so, both Main Battery and CMOS cell were gone.

    In June, 1997 I bought a Dell Latitude LM P133 and although it usually resided on on its Power Supply, the three-hour battery operation was often used and within 30 months, working battery life was below 20 minutes.

    In February 2000, I bought a Dell 'Spare-Parts' (re-conditioned) battery for the LM and since by then I also had reliable (Lind Power) DC Power Supply, it has been rarely operated to full depletion of that Main Battery.

    The battery is never 'removed' and almost always connected to AC or DC Power Supply, the charging program in the computer prevents 'over-charge' (check for 'over-heat' as a sign of 'over-charge').

    Now in its eighth year, that old battery will still provide nearly two hours of working operation and CMOS battery has had no problem on eleventh year.

    That LM now serves as a 'back-up' to a Dell Latitude D800 purchased three years ago, it also usually resides on external power and will still provide nearly the same 'working-time' on battery power as it did three years ago.


    Message Edited by Art on 09-04-2007 12:03 PM
  • Hello Art,
    Thank you for taking the time to reply to my post. Just so that I understated you correctly, I hope you don't mind if I confirmed some things that you've said
    * so the surge protector is not trickling electricity into my laptop's AC adapter when its switch is in the off position?

    * the green light of the AC adapter... I thought that even if it's not on, the electricity is still trickling through it. So no green light means ABSOLUTELY no electricity, note even the trickling ones that apparently goes through when you have the computer connected to the power outlet in the wall (with the computer turned off of course)?

    Thank you,
  • Calla,

    When there is no 'green' light, there is no power output available from the Power Supply. This is a useful check when traveling that you have selected an outlet with power

    There are some conditions when a 'mains' power interruption will leave the 'green' light out with 'mains' power connected and you must disconnect for a few seconds and reconnect, or end up with a dead battery (sort of a 're-set').

    You will also notice that the 'green' light will remain on for a few seconds after un-plugging' from main power.

    With Laptops switch off, there would still be a very small amount of current through the Power Supply to keep the 'clock' and that is what would 'save' the CMOS Cell. If the battery needs charging, the draw would be maximum.

    On my LM (with its power off), you see a steady light on Laptop Lid when charging and blinking when not. Don't recall any such signal from this D800, except when charging.

    I have four different brand Power Strips ('Surge Protector's) and when their switches are off, they have no power available, they also have 'indicator' lights to confirm when power is available to their outlets.