LiFePO4 can discharge in deep cold but must not be charged below freezing without heating: below about 0°C, and severely below −20°C, lithium plates onto the anode instead of entering it, which permanently loses capacity and can create internal shorts. Heating fixes that, at the cost of energy, heaters, sensors and BMS logic that can themselves fail.

Sodium-ion keeps far more of its capacity in the cold and charges safely at −20°C without heaters in our validation. It stores less energy per kilogram, so it suits starting and intermittently charged equipment better than long-range traction. More: Sodium-Ion vs Heated LFP: Why We Removed the Heating Pads.

A fleet of 50 electric excavators in the Oslo region ran standard 48V 400Ah LFP packs with no preheating and no low-temperature charge interlock. At −25°C, hydraulic pumps drew bursts up to 300A, the pack voltage sagged below the machine’s 36V undervoltage limit, and operators restarted machines four to five times a shift. Charging cold cells cost the packs about 30% of their capacity in one winter.

We redesigned the pack as a thermal-electrical system: polyimide heater films between modules (−25°C to 15°C in about 45 minutes on grid power), 3 mm aerogel insulation that held the core above 15°C through two idle hours at −25°C, and a BMS that routes incoming power to the heaters first and allows charging only above 15°C.