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    SXPS 16 Battery Won't Charge Above 99%

    Discussion in 'Dell XPS and Studio XPS' started by guitardude7, Jun 18, 2009.

  1. guitardude7

    guitardude7 Notebook Guru

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    Dell sent me a new battery for my SXPS 16 because the old battery was only lasting about an hour. I fully charged the new battery and drained it completely, then charged it back up all the way. I'm positive that the battery is fully charged, but the battery meter in windows is telling me that it's 99% charged. I thought that there was a problem with the new battery, so I put the old one back in and fully charged it; this time it tells me it's only 92% charged when i know it's 100% charged. Obviously, there is something wrong with the battery meter. Does anyone know how to recalibrate/reset it? Dell told me to update the bios and I did, but that did not work.
     
    guitardude7, Jun 18, 2009
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  2. Eambo

    Eambo Notebook Evangelist

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    Have you checked in the BIOS itself? The BIOS has it's own battery meter - see what it tells you in there. Press F2 on startup to access it.
     
    Eambo, Jun 18, 2009
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  3. ohnavi

    ohnavi Notebook Enthusiast

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    your not meant to drain your battery completely.

    you'll kill it like that.
     
    ohnavi, Jun 18, 2009
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  4. 7oby

    7oby Notebook Evangelist

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    You actually can't drain it completely - at least not with some effort.

    The reason is that if you set windows critical battery level to 0% (default dell is 5%) before it will shutdown or system to disk, that this 0% is an offset to an OEM predefined value.

    [​IMG]
    p. 48 (you can check older ACPI specs as well - they don't differ in this respect):
    http://www.acpi.info/DOWNLOADS/ACPIspec40.pdf

    The low capacity state is 1743mWh for my Dell battery:

    [​IMG]

    The ACPI Spec does mention several ways about how and when battery calibration is triggered. I didn't find a reference for how Dell exactly does it - neither in the user manual nor in their knowledge base. If you have one, I'm glad to read about it.

    But I found a reference to how HP does it. And basically they trigger calibration if the capacity is at 5%:
    http://h10025.www1.hp.com/ewfrf/wc/...oduct=18703&docname=c00596784#c00596784_calib

    That means if you change the 5% level to 10% and never drain your battery, then it might never get calibrated and the capacity meter might display very wrong values. But that's not for sure unless someone has an understanding which of the many calibration methods and parameters dell implemented.
     
    7oby, Jun 18, 2009
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