What kind of cooling system do EV batteries use and how does it work?

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Have you ever pulled into a fast charging station on a freezing morning without notifying your EV first, and found that it charges more slowly? Turns out that if you set that same charger as a destination in the car's navigation, many EVs will use the time it takes to drive there to prepare the battery. It's something Tesla's manual tells owners to do 30 to 45 minutes before arriving, while Porsche goes so far as to warn that, without doing so, a vehicle's charging power might be lower.

This warm-up routine is part of an EV battery's thermal management system in most modern cars. Alongside it is usually a cooling loop, which uses liquid coolant pumped via tubes or metal plates pressed against the battery, collecting heat and carrying it to a radiator or into the car's air conditioning system.

Fleet management company Geotab tracked more than 22,700 EVs for a study and found that, on average, batteries lost 2.3 percent of their health each year. Cars in hot climates lost about 0.4 percentage points more a year than those in mild ones, while cars that frequently used fast chargers above 100 kW lost 3 percent a year against 1.5 percent for those that rarely did.

At the average rate, a battery would still be at roughly 77 percent after a decade, in line with research suggesting that EV batteries can last much longer than experts first predicted. When fast charging, where 300 amps or more can be pushed through the battery pack, a lot of waste heat is generated and needs to be removed. In 2021, a review in the journal Energies found that more than a 5 degree Celsius temperature difference across a cell can speed up aging by 25 percent, meaning that a good cooling system has to keep the whole pack both balanced and regulated.

In a cold battery, internal resistance climbs, and fast charging one can cause lithium plating, a buildup of metallic lithium on the cell's electrodes that can get worse as temperatures drop. Recurrent, which studied more than 30,000 US EVs, found that batteries averaged 78 percent of their ideal range at freezing temperatures, and around 70 percent at -7 degrees Celsius. Cabin heating accounts for about two-thirds of the extra energy an EV uses in the cold.

The original Nissan Leaf, from way back in 2010, used passive air cooling for its 24 kWh pack, while Tesla, GM and Ford used liquid systems. Leaf owners in Phoenix tested 12 cars from the 2011 and 2012 model years and found range losses, which Nissan said affected fewer than 0.3 percent of US models, as noted by MIT Technology Review in 2012. The third-generation Leaf Nissan unveiled in 2025 finally switched to a liquid-cooled 75 kWh battery. The benefit of liquid cooling is that it needs two to three times less energy than air to hold a pack at the same temperature, according to Energies, and most EVs now use it as a result.

The engineers behind BMW's i3 decided to skip the coolant loop entirely, and instead opted to run refrigerant from its AC straight to the battery. British automaker McLaren went a step further with its Speedtail by submerging all its cells in an electrically insulated oil, a step it called a first for a production road car. Simulations cited in the Energies review found that immersion cooling like this could move heat up to three times better than cooling plates.

A battery's coolant loop will usually be linked to a radiator for light loads and, through a heat exchanger, to the car's air conditioning for heavier methods like fast charging. 

Let's take Nissan's thermal management system as an example: It switches between the two modes and routes heat from the charger into the battery during home charging, a feature that the newer Leaf model uses to warm it up. Tesla's Model Y, meanwhile, uses a valve nicknamed the "Octovalve" to move coolant between the motors, battery and electronics, as Jalopnik found following an engineering teardown. Tesla is also exploring a patent on running the drive motor inefficiently on purpose, so that its waste heat can warm the battery.

General Motors says that its Ultium heat pump collects waste heat from the battery, power electronics and even passengers' bodies to warm the cabin, which adds around 10 percent more range. China has recently introduced new rules that require new EVs to show that their batteries don't catch fire or blow up when a cell goes into thermal runaway. That requirement, however, depends on the pack's cooling and insulation stopping heat from spreading to other cells.