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BQ35100: State-of-health measurement for Li-MnO2

Part Number: BQ35100


Hi,
I have a question about Ti BQ35100 battery fuel gauge. We use it with a primary Li-Mn-O2 cell in the "State-of-health" mode.
I know it is difficult to determine this with this type of battery due to its flat discharge curve.
What I have observed is that the curve for the "State-of-health" is more like the curve for cell voltage than the predicted residual capacity.
I have done three different discharge tests with three different discharge intervals. One with only 5 seconds of relaxation time, one with 30 seconds and one with 10 minutes of relaxation time.
The conclusion is that all "State-of-health measurements" follow the value of the cell voltage rather than the capacity curve with the difference at what level the "plateau" is.
The first measurement with 5 seconds of relaxation time have a "plateau" level of 39%. The second measurement have a "plateau" level of 46% and the last with 65%.
The blue curve shows the cell voltage and the red curve symbolizes the theoretical optimal capacity left.
 
My question is, should the "State-of-health" value be somewhat linear to the remaining capacity of the battery?
I.e. Should the "State-of-health" value follow the red curve?
  • Hello Aivaras,

    I believe this may be a duplicate post: e2e.ti.com/.../976147

    The SOH should be linear line downward, if he discharges between wakeup is the same and it's the same time interval.

    SOH mode uses a very accurate voltage lookup to calculate SOH, therefore the battery voltage must be stabilized after discharge to get accurate results. There should be a couple hours of relax time before trying to take an OCV to calculate the SOH.

    Sincerely,

    Wyatt Keller