Tired of getting frustrating charging rate on fast chargers (18-25 kW) under cold weather conditions, we got together a group of Kona owners to do some reverse engineering to understand when the battery heater activates. First thing to know, the BMS uses the temperature of lowest battery module in its logic to activate the battery heater. We found 3 conditions for the heater to activate:
- The battery heater will come On if the SOC is less than 33% and battery temp is -5 degC or less. It goes off when battery reaches 5 degC. This seems to be for conditionning the battery for an eventual stop to a fast DC charger. The Winter Mode needs to be active for this to happen.
- It will also be active when charging on 240v depending on battery temp as well. At -15 degC, it will engage around 82% soc. At 0 degC, it will engage around 91%. At 5 degC, activates around 93%. The Winter mode doesn't need to be active for this.
- The battery will be active on fast charger as well. In most conditions, it will heat the battery upto to 15 degC depending of the starting % SOC. The battery will continu heating due to the heat lost during charging.
Good to know on fast chargers:
Battery temp < 1 degC : max power 18 kW
1 degC > Battery temp > 5 degC: max power 25 kW
5 degC > Battery temp > 15 degC : max power 40 kW
15 degC > Battery temp > 25 degC: max power 50 kW (50kW chargers) or 56 kW (>100kW chargers)
Battery temp > 25 degC: max power > 70 kW (>100kW chargers)
With battery temp as low as -20 degC, no heater activation was observed in other situations. It is believe that at much lower battery temp, the heater will activate to protect the battery. Minimum exterior temperature we had so far is about -25 degC.