Yeah one of the vendors I mentioned above sells batteries with exactly that functionality -- if the temperature is too low, the BMS disconnects and the heating

Yeah one of the vendors I mentioned above sells batteries with exactly that functionality -- if the temperature is too low, the BMS disconnects and the heating circuit is powered by the incoming energy (whatever the source might be) until the cells are warm enough: https://www.canbat.com/product/12v-100ah-cold-weather-lithium-battery/ https://www.canbat.com/product/12v-100ah-cold-weather-lithiu...