Short answer: winter range loss is mostly an energy budget problem, not a motor problem. At 50 km/h a typical EV may need only around 8–10 kW to move. Switch on a 4–6 kW resistive heater and you can add 40–60% to the total draw. Then add warm-up energy for the battery on every cold start, and short trips start to look terrible.
Our new video explains why the cold battery itself loses capacity and power. This post covers the other side: the arithmetic of where the kWh go. Watch the video first, then use the formulas below to estimate your own winter loss.
Key point: Range = usable kWh ÷ (Wh/km). In winter, the cold shrinks the numerator a little and the auxiliary loads push up the denominator a lot. And the slower or shorter you drive, the bigger the share those fixed loads take.
1. The core formula: fixed loads divided by speed
Energy per km is just total power divided by speed:
E (Wh/km) = (Pdrive(v) + Pheat + Paux) ÷ v (km/h) × 1000
Illustrative assumptions (not measured data): Pdrive = 8 kW at 50 km/h, 18 kW at 110 km/h; heater = 5 kW; other aux loads = 0.3 kW.
- City, 50 km/h: summer (8.3 ÷ 50) = 166 Wh/km. Winter (13.3 ÷ 50) = 266 Wh/km, which is about 38% less range.
- Highway, 110 km/h: summer (18.3 ÷ 110) = 166 Wh/km. Winter (23.3 ÷ 110) = 212 Wh/km, which is about 21% less range.
The same 5 kW heater costs about twice as much range in town as on the highway, because at low speed it runs for more hours per km. That is why winter city range often feels worse than the EPA figure suggests. For a closer look at the highway side, see Why Does EV Range Drop So Fast on the Highway? 70 vs 80 MPH Tested.
2. Heat pump COP vs PTC: the electrical kW is what counts
The cabin needs a certain amount of thermal power, Q. What the battery actually pays is the electrical power:
Pelec = Q ÷ COP (PTC: COP ≈ 1; heat pump: COP > 1, falling as it gets colder)
Illustrative case: the cabin needs Q = 4 kW. A PTC heater draws about 4 kW. A heat pump with a COP of 2.5 (mild cold) draws 1.6 kW. At a COP of about 1.5 (deep cold) it draws about 2.7 kW. Feeding that into the formula from point 1 at 50 km/h, the heat pump at COP 2.5 saves about 48 Wh/km compared with PTC. The colder it gets, the smaller the advantage, and many systems blend in resistive heat at very low ambient temperatures (COP values are typical textbook ranges; check each model's spec, to verify).
This is the same COP math as summer A/C, just running in the other direction. We tested the cooling case in Does EV Air Conditioning Kill Your Range?. Heating is usually the harder case: in the cold, the temperature difference between cabin and outside air is larger and the COP is lower.
3. Battery warm-up energy: a one-time cost per trip
Warming a pack takes sensible heat:
Ewarm = m × cp × ΔT ÷ 3600 (kWh, with m in kg, cp in kJ/kg·K)
Illustrative case: a 450 kg pack, cp ≈ 1.0 kJ/kg·K (a rough assumption for cells plus housing, to verify), warmed from −5 °C to 15 °C (ΔT = 20 K) needs 450 × 1.0 × 20 ÷ 3600 ≈ 2.5 kWh of heat. That is before counting losses.
Spread over a 10 km trip, that adds 250 Wh/km, more than the whole summer driving consumption. Over a 200 km trip it adds only 12.5 Wh/km. This is why preconditioning on the charger matters: the warm-up energy comes from the grid, not from your range. (The electrochemistry of why the cold pack needs warming is in the video.)
4. I²R: higher resistance costs energy and peak power
The pack's internal resistance turns part of every amp into heat:
Ploss = I² × Rint I ≈ P ÷ Vpack
Illustrative case: a 400 V pack delivering 20 kW draws I ≈ 50 A. At a warm Rint of 0.1 Ω the loss is 50² × 0.1 = 250 W (1.25%). If the cold triples Rint to 0.3 Ω, the loss becomes 750 W (3.75%). The resistance values are assumptions for illustration; real packs vary widely (to verify per pack).
At cruise, that loss is small next to the heater, and it also warms the cells. The bigger effect is voltage sag (ΔV = I × R) during hard acceleration, which makes the BMS cap power and regen. So I²R hurts performance more than it hurts range at a steady cruise.
To verify: all kW, COP, mass and resistance figures above are illustrative assumptions for the math, not specs of any particular car. For real-world benchmarks, AAA's 2019 cold-weather test reported that at 20 °F (−7 °C), average range fell about 12% with HVAC off and about 41% with the cabin heater on (AAA Newsroom). Newer heat-pump EVs may do better; check model-specific data.
Putting it together
Winter range loss ≈ fixed heater load (biggest at low speed) + warm-up energy (biggest on short trips) + a small I²R and capacity penalty from the cold cells. Practical levers, in engineering order: precondition while plugged in, use seat and wheel heaters (tens to a few hundred watts) instead of heating the whole cabin air (kW), and combine short errands into one trip.
For the full story of what happens inside the cold battery, watch Why Do EVs Lose So Much Range in Winter? It's NOT the Motor! Cold Battery Explained. Related: Does EV Air Conditioning Kill Your Range?
What is your winter Wh/km compared with summer: city or highway? Drop the numbers in the comments.
