A warm day is usually good news for your range. Fast charging can be slower, though, especially if you have been driving at high speed for hours. Here is why that happens and what you can do about it.
Your range stays good
A warm battery works smoothly, and you do not need to heat the cabin. Only the air conditioning draws power.
A worked example with assumed figures: the air con draws 1 kW on average and you drive for two hours. That is 2 kWh. If your car uses 18 kWh per 100 km, the air con costs you about 11 km of range. In winter that loss is usually bigger, as you can read in winter range and charging. Your own numbers will differ, so check your trip computer to see what the air con really uses.
Why heat slows down fast charging
Driving and charging both warm up the battery. The faster you charge, the more heat builds up. If the battery gets too hot, the car lowers the charging power itself to protect the cells. You see this as a power level below what the charger can deliver.
It mostly happens when you plug into a fast charger straight after a long drive on a hot day. How strong the effect is depends on your car and its battery cooling. Some cars cool the battery actively, others far less.
An example with assumed figures: you need to add 40 kWh. If the car averages 100 kW, that takes 24 minutes (40 divided by 100, times 60). If heat limits the average to 60 kW, it takes 40 minutes. That is 16 minutes extra, and a more powerful charger changes nothing, because the car sets the pace. Why the power drops during a session anyway is explained in the charging curve.
What can you do?
- If you have been driving hard for a while, ease off for the last few kilometres before your stop. A battery that arrives less hot can fast charge for longer.
- Park in the shade at the charger if you have a choice.
- Leave the air con on while you charge, if the car allows it. Many cars also cool the battery actively, and that takes power.
- Plan your stops for the cooler part of the day if you have a long drive ahead, for example in the morning or late afternoon.
- Check how many kW the car draws shortly after plugging in. If it is well below what you expected, you know the heat is playing a part and the charger is not at fault.
Pre-cooling
Just like pre-heating in winter, you can pre-cool the cabin in summer while the car is plugged in. Whether your car can do this, and how to set it up, depends on the car and its app. The benefit is simple: the power comes from the charger, not from your battery, and you get into a cool car.
It works at a home wallbox, and also at a public charger during a stop, as long as the car stays connected.
Common mistakes
- Switching the air con off while charging to save power. In many cars that actually costs charging speed, because the battery is cooled less.
- Assuming the charger is faulty. A slow session on a hot day is often the car protecting itself. Only switch chargers if the power stays low after a while.
- Looking for a more powerful fast charger in the hope of getting faster. If the car limits the power, you gain nothing.
When heat hardly matters
If you charge calmly at a wallbox or an ordinary AC charger, far less heat builds up in the battery and you will notice little. The same goes for short city trips: the battery rarely overheats. The problem is mainly fast charging after a long, fast drive.
Charging in full sun
Cables and plugs are made to hang outdoors, so sun in itself is not a problem. A plug or cable that has lain in the sun for hours can get quite hot, though. Pick it up carefully and wear gloves if you like.
Looking for a covered charging spot? On the map you will find chargers at shopping centres and car parks, and the fast chargers page shows where the power is high.