To mitigate issues with cold weather, 2nd generation Nissan Leaf battery packs with the 'cold weather package' include a 'battery warmer' between banks. This is controlled via the BMS which was already monitoring temperature with some thermistors. It's a resistive element like that used in heated seats or an electric blanket.
The Tesla battery is a liquid cooled battery and thus can be warmed via coolant that is heated by the inductive heater for the HVAC. Same for the GM Volt/Bolt.
The Tesla battery is a liquid cooled battery and thus can be warmed via coolant that is heated by the inductive heater for the HVAC. Same for the GM Volt/Bolt.