Have a look at Electric impedance spectroscopy- https://en.wikipedia.org/wiki/Dielectric_spectroscopy https://en.wikipedia.org/wiki/Dielectric_spectroscopy The

Have a look at Electric impedance spectroscopy- https://en.wikipedia.org/wiki/Dielectric_spectroscopy https://en.wikipedia.org/wiki/Dielectric_spectroscopy Theres a handfull of Tier 1 BMS chips that support it already. though, half of them are meant for traction/EV packs instead of BESS.