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BQ27531-G1: BQ27531-G1: How to calculate state of health (SOH)?

Janhavi Rane
Prodigy 170 points
Part Number: BQ27531-G1

Hello,

I am using BQ27531-G1 gas gauge. As per the Technical reference manual of gauge (SLUUA96A) , SOH is expressed as a percentage of the ratio of predicted FCC(25°C ,SOH LoadI) over the DesignCapacity(). In our case, FCC= 3771 mAh , SOH LoadI= -200 mA and Design capacity = 4400 mAh (Please refer attached image of BQ studio). 

SOH= 3771/4400= 0.8570= approx. 85%

but in BQ studio SOH shows 92 %. Why?  Here the value of FCC which we have consider is correct? How to calculate SOH?

Regards,

Janhavi Rane

  • 0
    TI__Guru** 105590 points

    Hello Janhavi,

    The FCC reported by the gauge is not the same as the FCC used for the SOH calculations. As the TRM mentions the gauge will do a discharge simulation with the preset temperature and current, using the Ra and Qmax values the gauge learns it will find the SOH FCC value and use that as the numerator in the equation.

    The FCC reported by the gauge uses the load select/ load mode values for discharge simulations.

    Sincerely,

    Wyatt Keller