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Charging problem on Compaq Presario 1200

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  • Charging problem on Compaq Presario 1200

    I have a problem with a Compaq Presario 1200, it has a charging problem for a long time. I always thought that the battery was losing efficency and a normal wear for computer battery, until I dicided to buy a new battery (in fact 2 batteries).

    When I inserted a new battery in it, it started to charge for about 10 minutes then stopped with only 1 or 2 percents gain in capacity. I pulled it out and put it back in again, same problem. I thought... just bad luck... a faulty battery, let's try the other one. Same thing happened again with this one.

    In fact I was more successful with the old battery. The original battery is a 3600 mAh, and the new batteries are 4400 mAh. Maybe it has something to do with the fact that the charge time is shorter than the original.

    With the old battery, I managed to get a full charge by re-inserting it several times, getting a few percents everytime. Once, it was at about 55% then after re-inserting the battery, it was suddenly at 100%. An other time, it was at full charge then I let the computer run on the battery for a full discharge. The computer was set to hibernate when reaching 2%. At 83% and 15 minute running time, it suddenly hibernate. I thought that's impossible, I then push the power button, still on battery. After being back in Windows, BatteryMon and Windows were both showing 83%. After looking at BatteryMon's log, I can see 1 or 2 samplings of 2%. What happened? I can't explain but the computer ran for over 45 minutes with the remaining 83%.

    My question is ..., what parts of the computer is involved in the charging process? By the way, I forgot to mention that I also replaced the charging module in the computer, which is attached to the main board (plugged in). I also tried another power supply in case the voltage was dropping. But none of these has changed the result.

    Since computers charge their battery even when the computer is turned off, the main board is certainly not in the equation. The only part involved should be the charging module, power supply and the battery itself.

    Thanks to anyone who could light me up on this mystery.


  • #2
    Most laptop batteries are "Smart" batteries. This means that inside the battery pack there is a small circuit board. Which holds some ROM, with hard coded data about the battery, and the facility to communicate to the charging circuit (via a serial connection called the SMBUS).

    The charging circuit, which is normally on the motherboard, listens to the data coming from the battery via the SMBUS, and then takes the actions required to charge that type of battery.

    While this might be interesting background information, it doesn't explain why the charge level reported by the battery pack dropped so suddenly from 83% to 2% then back up again.

    Batteries are notoriously unreliable however.


    • #3
      Since the system is not working with any of the 3 batteries, shouldn't this fact be excluding the batteries from the equation and leaving the charging circuit as responsible?

      I mentioned that I replaced what they call the changing module which holds a lot of electronic parts and is connected to the motherboard through a 20-pin connector.

      Would it be possible that there is another part of the changing circuit on the motherboard?
      Last edited by carbo; 04-14-2007, 05:18 AM.


      • #4
        It is hard to say with 100% certainty if the batteries are at fault, or not.

        If they were new original Compaq batteries made especially for this machine I would agree. But with after market batteries you never know if they are really compatible units or not.

        One of the ideas of the smart batteries was to improve compatibility because it allowed the battery to give enough details to the charging circuit, to allow the charging circuit to know how to charge that battery type.

        But of course great compatibility, means great competition and manufacturers don't like competition. So compatibility was broken (or ignored) in order to sell original batteries at higher prices. Imagine how different it would be if there was a standard laptop battery. Like a 'D' cell is a standard.


        • #5
          When the battery is charging but nearing 100%, the green light flashes slowly instead of being steady. Since I got this charging problem I must admit that it probably rarely happens, but it happened yesterday.

          So this morning it came to my attention when looking at the green light indicating charging status, that the light was always flashing fast for as long as I can remember having this charging problem. It might be important to say that without BatteryMon showing me the charge rate, I couldn't say for sure if it is really charging or not, because Windows always says it is charging when not at 100%, it never says that the battery is at fault.

          I never mentioned it, but when the battery stops charging before reaching 100%, the green light starts flashing when the charge rate falls to zero, which was dropping slowly from the beginning of the charging process.

          So when I re-insert the battery or switch on battery powered mode, I only reset the fault and soon the charging circuit detect a faulty battery. For what happens with the new batteries, I would then agree with you with the fact that the incompatibility is responsible, so the original battery would have an intermittent problem, along with a normal degradation.
          Last edited by carbo; 04-15-2007, 02:38 PM.