WattCold weather EV charging
I live where it hits minus twenty. Here's what the cold actually does — separated into the three different problems people usually mash together.
Three separate losses, not one
Almost every "EVs lose range in winter" article treats this as a single effect. It isn't, and the distinction matters because two of the three are things you can manage.
1. Cabin heating — the big one
Moving a person-sized volume of air from freezing to comfortable takes real energy, and unlike a combustion car there's no waste engine heat to scavenge. A heat pump helps a lot down to roughly 20°F; below that most systems fall back to resistive heating, which is where the consumption spikes. This is the largest single loss on a short trip and it barely matters on a long one, because it's mostly a fixed cost paid at the start.
2. Battery chemistry — temporary
Cold lithium cells have higher internal resistance. You get less usable capacity and less power, and the pack will limit both charging and regen until it warms. Nothing is wrong and nothing is permanently lost — the range comes back when the pack does.
3. Charging speed — the one that surprises people
A cold pack throttles charge acceptance hard. On DC fast charging this is dramatic: a pack at 20°F may accept a fraction of its rated rate until it warms up, which is why a winter road trip stop can take twice as long as the same stop in July. On AC charging at home it matters less, because 7kW is well under what even a cold pack will take.
What this means for generator charging
Good news, oddly. Generator charging happens at 16–32A, which is slow enough that a cold pack's acceptance limit is rarely the binding constraint. Your generator is the bottleneck, not the battery temperature. What does change is the conversion: the same kWh buys fewer miles. Plan on roughly a third less range per hour of charging than the mild-weather number. The calculator has a cold setting →
How much range do you actually lose?
| Conditions | Typical efficiency | Range vs mild |
|---|---|---|
| Mild, 60–75°F | 3.5–4.0 mi/kWh | baseline |
| Cool, 40–50°F | 3.0–3.4 mi/kWh | -10 to -15% |
| Freezing, 20–32°F | 2.5–3.0 mi/kWh | -25 to -30% |
| Deep cold, below 10°F | 2.0–2.5 mi/kWh | -35 to -45% |
Short trips land at the bad end of each band; highway runs at the good end, because the heating cost is amortised over more miles. Wind and unplowed snow make it worse than any table predicts.
What actually helps
- Precondition while plugged in. Warming the cabin and pack on shore power instead of on the battery is the single highest-value habit in winter. Free miles, effectively.
- Leave it plugged in when parked. Not to charge — so the pack can keep itself warm on grid power rather than eating its own range.
- Use seat and wheel heaters first. Heating a body directly is dramatically cheaper than heating the air around it.
- Set a departure time. Scheduled preconditioning does this automatically and beats remembering.
- Charge to a higher percentage in winter. Your buffer is smaller than the display implies once the heater is running.
Don't panic about the range display. A cold pack under-reports because it's estimating from current conditions. It recovers as the pack warms. The capacity isn't gone, it's asleep.
Outage season is winter
The uncomfortable overlap: the time of year you're most likely to lose power is also when your car has the least range and charges the slowest. If your outage plan is a generator, the winter numbers are the ones to plan against — not the summer ones on the box.
Sizing a generator → · Why inverter output matters →