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Dell laptop battery failure mode

Discussion in 'Electronic Repair' started by tom_mc_h, Apr 15, 2004.

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  1. tom_mc_h

    tom_mc_h Guest

    Hi-
    I have an old Dell XPi-CD laptop. It *seems* that the battery is bad.
    But I am not sure if it is the battery or some other problem.

    Here is how it acts:
    It will not boot with the battery installed and the charger plugged
    in. (I have tried other power supplies and they all act the same).
    When I try to turn it on the leds flash, it starts to whirr a little
    and very very briefly the first screen flashes on with some bios info
    (so quickly it is hard to read) then everything shuts down, no led's,
    nothing.

    After charging the battery a while, I can read the terminal voltage
    but it drops off very quickly (Thats with a dvm - no load). I busted
    open the case, and tested each cell individually, with a 6v automotive
    bulb and each cell seems to be ok - they all light the bulb fairly
    well. That makes me conclude that maybe something is wrong with the
    built-in battery control circuitry. Is this a reasonable assumption?
    Isnt it true too, that if a cell is bad the laptop will still function
    with the power supply?

    Can anybody give me some advice on what these symptons indicate? I
    dont want to spend money on a battery for this old laptop then find
    out there is some other, more grevious, problem.

    Thanx
    Tom
     
  2. I was just wondering myself about the failure rate of the circuitry
    in those battery packs.

    I got a Mac Powerbook 1400C last fall real cheap, and only got around
    to looking at it this week (well, there was no AC adaptor, and I was
    unsure of the details. When I got enough, I pulled the 24VDC switching
    supply out of a Cannon inkjet printer I found in the garbage last fall,
    and it runs fine).

    In my case, the laptop runs without the batter. But, it was telling
    me the battery wasn't installed. Not "bad", but not there. Someone
    had written on the battery that it didn't work, and might be bad.

    I figured it might be internal logic that wasn't working. So I
    too opened the case. Oddly, the top 3 or 4 Nimh batteries of the chain
    showed a bit of voltage, and the rest showed nothing. I charged up
    the lower half, using a resistor that wouldn't allow more than about
    30mA, and they came back. So I connected that "charger" to the whole
    string, and they came up, after a bit. So I dropped the resistor,
    charged some more, then dropped the resistor value again, and charged
    some more. The PIC was showing a different output on the battery connector,
    so there was hope.

    I stuff the battery back together, and jam it back in the laptop. To
    my amazement (since I only pumped a bit of current into it, and not
    for particularly long) the computer ran without the AC adaptor. Get
    the contrast right, and the battery indicator makes it look good.
    I had it on for about half an hour, and all seemed well.

    This morning, it wouldn't start without the adaptor. And it's saying
    again that the battery is not there. I haven't gotten any further.

    So you might try slowly charging the batteries outside the laptop,
    using low current, and then see if that runs it. One might hope
    that if the battery charges, it would be good enough for you to
    check out the laptop.

    Except that I don't know what the exact function of that built
    in circuitry, you might also try powering the laptop with a DC supply
    feeding the terminals of the laptop where the battery normally connects.
    See if that powers it.

    Michael
     
  3. Mike

    Mike Guest

    Macintosh machines are a whole different ballgame when it comes to
    batteries.

    There is an extention along with a program you can download called
    "Intelligent Battery Recondition" It supposidly updates the firmware in the
    battery that doesnt let the cells dip so low, and it also "precharges the
    battery" to get the control logic functioning again so it can perform the
    update.
     
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