[Bug 255] New: battery voltage scale is not correct

bugzilla-daemon at bugzilla.openmoko.org bugzilla-daemon at bugzilla.openmoko.org
Sun Mar 11 14:44:24 CET 2007


           Summary: battery voltage scale is not correct
           Product: OpenMoko
           Version: current svn head
          Platform: Neo1973
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: kernel
        AssignedTo: tony_tu at fiwin.com.tw
        ReportedBy: laforge at openmoko.org
                CC: sean_chiang at fic.com.tw

Since we don't have a coulomb-counting battery gas gauge, we cannot give proper
battery metering.

Our current battery percentage reading is based on battery voltage, and uses a
linear scale between 2.8 and 4.2V (see drivers/i2c/pcf50606.c:battvolt_scale()).

This scaling is obviously wrong and just a 'proof of concept' scale.  

Somebody needs to do proper charge/discharge measurements and come up with a
non-linear algorithm expressing estimated battery life based on present battery
terminal voltage.

This needs a lot of experimentation/measurement, as well as a couple of
calculations.  Please provide me either with a patch against battvolt_scale(),
or give me a mathematical formula expressing battery lifetime percentage as
function of terminal voltage.

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