BQ40Z50-R2: SOH accuracy

Hello,

The expectation of <1% SOH drop after 50 cycles (30%–80% SOC, ~23 equivalent full cycles) is reasonable for modern Li-ion cells like the MOLI INR18650M35A, especially at a reduced 4.1V charge voltage, which minimizes electrolyte degradation and SEI growth.

Actual cell degradation under these conditions should be minimal (likely <0.5% capacity loss), so the observed 2% drop and 3% increase are almost certainly due to algorithmic errors rather than physical cell aging. 
Make sure you have periodical Qmax and Ra updates every certain period of time (e.g. every 50 cycles or so)

Validate the actual capacity loss using a precision battery tester (e.g., discharge from 4.1V to cutoff at 0.2C before and after the 50-cycle test). This can confirm whether the SOH changes reflect real degradation or IC miscalculations.

If the actual capacity loss is <1%, focus on optimizing the IC’s configuration and calibration to align the SOH with the true cell state. 

Hello Jose:

Yes, I would agree this could be an algorithm error. Do you have any suggestions to improve the algorithm result? The SOH load is set to 5hrs, which is close to the use case.

 SW02172R03.gg.csv

The GG file is attached as well.

We understand several parameters can impact SOH, but FCC should be the most important one, and the FCC may have some offset. For example, in sample 9：

First calibration cycle: FCC = 2557

50 cycles

Second calibration cycle: FCC = 2743

And SOH increased with FCC.

Thank you!

Chen