If this is your first winter with an EV, you may have noticed that charging is slower at low outdoor temperatures than in summer. In this article we explain why, and whether there is anything you can do. First, a bit of dry theory.
What is BMS (Battery Management System)?
As the name suggests, this is the system that manages the battery. It has many responsibilities, but two main goals drive its decisions, in this order:
- Safety
- Long battery life
In short, the BMS protects the battery. During charging, the charging process is managed primarily by the BMS, not by the charging station. The station is generally ready to deliver as much power as the vehicle requests.
The BMS is the main reason EVs usually charge slower in winter. It can also preheat the battery for charging, which we discuss below.
Why outdoor temperature matters
Batteries perform best when cell temperature is roughly between 20C and 40C. That is their comfortable operating range, similar to how internal combustion engines have their own optimal temperature range.
| Powertrain | Typical optimal operating temperature |
|---|---|
| ICE (internal combustion engine) | 80C - 110C |
| EV battery | 20C - 40C |
During high-power charging, battery temperature around body temperature (35C+) is usually helpful. For some chemistries (for example certain Tesla packs), even higher temperature can be targeted to unlock peak charging speed.
In winter, when ambient temperature is near or below 0C, it is much harder for the battery to stay in that ideal range. So the car will try to keep the battery safe (for example above very low temperatures), but it usually will not keep it at fast-charging-optimal temperature all the time, because that would consume too much energy when charging may not even be planned.
What can we do about it?
It is important to note that simply driving (even at highway speed) may not heat the battery as much as many expect, because EV drivetrains are efficient.
For cars with charging pre-conditioning
If your EV supports charging pre-conditioning, set your charging stop in the built-in navigation. The car estimates current battery temperature, travel time and heating needs, then prepares the battery so it arrives closer to the desired charging temperature.
Keep in mind that raising battery temperature significantly can take time, especially on larger packs.
For cars without charging pre-conditioning
If your car does not support pre-conditioning for charging, you will usually have to accept slower winter charging. Once charging starts, the car will still begin active battery heating, but this takes time.
