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BQ20Z95: BQ20z95 FCC Error

Jeffrey Chase
Intellectual 510 points

Part Number: BQ20Z95

We have received a battery from one of our customers that was reporting an FCC of about 2/3 of what it should have. The battery is a 6600mAh battery, but came back reporting an FCC of 4375mAh. The RSOC and ASOC, understandably, varied widely with an ASOC of 61 and an RSOC of 92%. The cells were all at around 4102mV, so the battery should have been at least close to fully charged. A screen shot of the SMBUS data is shown below.

The battery was cycled once, and the FCC reported 6499mAh, and RSOC and ASOC were then equal. Nothing else was done to the battery other than the cycle.

The battery only has 15 cycles on it, and the customer does not know of any unusual circumstances with the use history. Are you aware of any circumstances in which the FCC can be miscalculated by the gas gauge by this degree?

  • 0
    TI__Guru* 76230 points
    Hi Jeffrey,
    It could be that your cells were cycled at low temperature. At low temperature, FCC reduces which is an inherent characteristic of a battery. The fact that you cycled the battery once and it recovers is indicative that that is likely what happened.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 510 points

    Ran a test on this battery at the lowest temperature reported in lifetime data. Did not repeat the same loss of capacity. I've included the Ra Tables from this battery with the initial values ("Golden"), what they were when the battery was returned with the low FCC, and what they were after a cycle had been applied. Is there anything that can be discerned from this information? I noticed there is a large difference in values between the "Golden" and As Received as well as between the As Received and After Single Cycle.

    [R_a0(Ra Table)] "Golden" As Received After Single Cycle
    Cell0 R_a flag  0000  0000  0000
    Cell0 R_a 0  138  136  146
    Cell0 R_a 1  138  136  146
    Cell0 R_a 2  155  160  179
    Cell0 R_a 3  208  195  216
    Cell0 R_a 4  429  179  446
    Cell0 R_a 5  706  156  734
    Cell0 R_a 6  1599  176  1662
    Cell0 R_a 7  2243  190  2331
    Cell0 R_a 8  2416  205  2511
    Cell0 R_a 9  3120  268  3243
    Cell0 R_a 10  5122  426  5324
    Cell0 R_a 11  6316  581  6564
    Cell0 R_a 12  2664  567  2768
    Cell0 R_a 13  5028  807  5225
    Cell0 R_a 14  6205  996  6449
    [R_a1(Ra Table)]      
    Cell1 R_a flag  0000  0000  0000
    Cell1 R_a 0  144  138  153
    Cell1 R_a 1  144  138  153
    Cell1 R_a 2  165  165  185
    Cell1 R_a 3  217  198  230
    Cell1 R_a 4  485  184  515
    Cell1 R_a 5   765  161  813
    Cell1 R_a 6  1687  181  1794
    Cell1 R_a 7  2355  198  2504
    Cell1 R_a 8  2527  211  2686
    Cell1 R_a 9  3291  277  3499
    Cell1 R_a 10  5449  446  5794
    Cell1 R_a 11  6693  588  7116
    Cell1 R_a 12  2898  587  3081
    Cell1 R_a 13  5271  803  5604
    Cell1 R_a 14  6481  989  6890
    [R_a2(Ra Table)]      
    Cell2 R_a flag  0000  0000  0000
    Cell2 R_a 0  138  136  151
    Cell2 R_a 1  138  136  151
    Cell2 R_a 2  161  162  185
    Cell2 R_a 3  213  198  230
    Cell2 R_a 4  504  182  544
    Cell2 R_a 5  747  158  807
    Cell2 R_a 6  1739  176  1878
    Cell2 R_a 7  2416  195  2608
    Cell2 R_a 8  2615  205  2823
    Cell2 R_a 9  3405  268  3677
    Cell2 R_a 10  5528  432  5969
    Cell2 R_a 11  6888  588  7437
    Cell2 R_a 12  2858  587  3086
    Cell2 R_a 13  5049  820  5451
    Cell2 R_a 14  6241  1014  6739
    [R_a3(Ra Table)]      
    Cell3 R_a flag  0055  0000  0055
    Cell3 R_a 0  236  140  156
    Cell3 R_a 1  236  140  156
    Cell3 R_a 2  270  165  185
    Cell3 R_a 3  372  200  233
    Cell3 R_a 4  674  187  224
    Cell3 R_a 5  1052  164  349
    Cell3 R_a 6  2293  181  761
    Cell3 R_a 7  3188  198  1058
    Cell3 R_a 8  3420  211  1135
    Cell3 R_a 9  4528  272  1503
    Cell3 R_a 10  7385  439  2451
    Cell3 R_a 11  9075  610  3012
    Cell3 R_a 12  3950  623  1311
    Cell3 R_a 13  7259  782  2409
    Cell3 R_a 14  8999  969  2987
    [R_a0x(Ra Table)]      
    xCell0 R_a flag  0055  0055  0055
    xCell0 R_a 0  221  136  146
    xCell0 R_a 1  221  136  146
    xCell0 R_a 2  248  160  179
    xCell0 R_a 3  333  195  216
    xCell0 R_a 4  687  179  206
    xCell0 R_a 5  1131  156  339
    xCell0 R_a 6  2561  176  768
    xCell0 R_a 7  3592  190  1077
    xCell0 R_a 8  3869  205  1160
    xCell0 R_a 9  4997  268  1498
    xCell0 R_a 10  8203  426  2459
    xCell0 R_a 11  10115  581  3032
    xCell0 R_a 12  4266  567  1278
    xCell0 R_a 13  8052  1071  2413
    xCell0 R_a 14  9937  1322  2979
    [R_a1x(Ra Table)]      
    xCell1 R_a flag  0055  0055  0055
    xCell1 R_a 0  233  138  153
    xCell1 R_a 1  233  138  153
    xCell1 R_a 2  267  165  185
    xCell1 R_a 3  351  198  230
    xCell1 R_a 4  785  184  212
    xCell1 R_a 5  1238  161  335
    xCell1 R_a 6  2730  181  739
    xCell1 R_a 7  3811  198  1031
    xCell1 R_a 8  4089  211  1106
    xCell1 R_a 9  5325  277  1440
    xCell1 R_a 10  8817  446  2385
    xCell1 R_a 11  10830  588  2929
    xCell1 R_a 12  4689  587  1268
    xCell1 R_a 13  8529  1068  2307
    xCell1 R_a 14  10487  1315  2836
    [R_a2x(Ra Table)]      
    xCell2 R_a flag  0055  0055  0055
    xCell2 R_a 0  227  136  151
    xCell2 R_a 1  227  136  151
    xCell2 R_a 2  265  162  185
    xCell2 R_a 3  350  198  230
    xCell2 R_a 4  829  182  215
    xCell2 R_a 5  1229  158  319
    xCell2 R_a 6  2861  176  742
    xCell2 R_a 7  3974  195  1031
    xCell2 R_a 8  4301  205  1116
    xCell2 R_a 9  5601  268  1453
    xCell2 R_a 10  9093  432  2359
    xCell2 R_a 11  11330  588  2939
    xCell2 R_a 12  4701  587  1220
    xCell2 R_a 13  8305  1038  2154
    xCell2 R_a 14  10266  1284  2663
    [R_a3x(Ra Table)]      
    xCell3 R_a flag  0000  0055  0000
    xCell3 R_a 0  144  140  156
    xCell3 R_a 1  144  140  156
    xCell3 R_a 2  165  165  185
    xCell3 R_a 3  227  200  233
    xCell3 R_a 4  411  187  422
    xCell3 R_a 5  642  164  657
    xCell3 R_a 6  1399  181  1434
    xCell3 R_a 7  1945  198  1993
    xCell3 R_a 8  2087  211  2139
    xCell3 R_a 9  2763  272  2831
    xCell3 R_a 10  4506  439  4618
    xCell3 R_a 11  5537  610  5675
    xCell3 R_a 12  2410  623  2470
    xCell3 R_a 13  4429  1142  4539
    xCell3 R_a 14  5491  1415  5627
  • 0 in reply to Jeffrey Chase
    TI__Guru* 76230 points

    Hi 

    Your later half of your  resistance table  learned to much lower values in the case where FCC was low. I am not sure why that happened but perhaps you may need to optimize the resistance tables  (Rb) which are hidden parameters for low temperature performance using our online tool gpcrb.

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Intellectual 510 points
    If this was seen on a higher population, I would be right there with you. We have made over 60,000 of these, and this has been the only case where this has happened so far. It's still possible that the tables aren't optimized. I'll look into using the tool.
    In the meantime, maybe I'm misunderstanding the tables. Based on the tech manual, these values are measured in 2^-10 ohms. That means the resistance values for the low FCC battery would have a lower resistance. Wouldn't lower resistance normally translate to higher capacity, not lower?