As mentioned in ‣, unfortunately, even if one cell in a cell group degrades unusually rapidly, we are unlikely to detect this easily. The only two cell parameters that should be detectable even from cellgroup data are self-discharge rate and Coulombic efficiency because normally they should be ~0 and ~1, respectively, but one faulty cells can have dozens or hundred times higher than values, and this should be discernable on cellgroup level (28 cells).

Also, both these conditions are important to alert on, because a high self-discharge rate probably indicates a short that might evolve into thermal runaway, and low Coulombic efficiency indicates active parasitic reactions, which might also lead to thermal runaway or venting if one of the reaction products is gas.

The remaining capacity of the cellgroup, average internal resistance, self-discharge rate, and Coulombic efficiency should be estimated all at once to avoid biases and double-accounting because cellgroup has just one output signal: voltage.

Part of Battery safety.

Related:

• Onboard BMS needs to know the degradation parameters to improve safety and prolong the battery’s life

See also:

• Cell voltage dips upon a soft short