Electric vehicles and hybrid electric vehicles use several distinct cooling systems to manage heat across the battery pack, electric motor, power electronics, and cabin. The most common types are air cooling, liquid cooling with glycol-based coolant, direct refrigerant cooling, and immersion cooling. Each approach balances cost, complexity, and thermal performance differently, and many modern EVs combine more than one in a single vehicle.
All of these systems exist because lithium-ion batteries perform best within a narrow temperature window of roughly 15 to 35°C (59 to 95°F). Above 50 to 60°C, safety risks increase significantly. Keeping batteries, inverters, and motors within safe operating temperatures is what determines how far you can drive, how fast you can charge, and how long the battery lasts.
Air Cooling
Air cooling is the simplest thermal management approach. In a passive setup, the battery pack relies on natural airflow and the surrounding structure to dissipate heat, with no fans or pumps drawing energy. Active air cooling adds fans that push cabin or outside air across the battery cells, giving more control over temperatures.
The main advantages of air cooling are its straightforward design, zero risk of coolant leaks, and minimal maintenance. It works well enough for mild climates and smaller battery packs, which is why it has appeared in some earlier-generation EVs and many hybrid vehicles where the battery is smaller and generates less heat. The downside is limited cooling capacity: air simply can’t pull heat away from cells as quickly as a liquid can, especially during fast charging or sustained high-power driving in hot weather. Over a 10-year span, battery capacity loss with air cooling lands around 7.2%, slightly higher than more advanced methods.
Indirect Liquid Cooling
The most widely used system in modern EVs is indirect liquid cooling. A mixture of water and glycol (similar to engine coolant in a conventional car) circulates through channels in a cooling plate or jacket that sits against the battery cells. The coolant absorbs heat from the cells, carries it to a heat exchanger or chiller, rejects the heat to the outside air, and loops back.
Water-glycol solutions have much higher thermal conductivity than oils, meaning they transfer heat efficiently. They also have low viscosity, so the pump doesn’t need to work as hard to push coolant through the system. This makes indirect liquid cooling a good balance of performance and energy cost. It’s the standard for most major EV platforms today.
The tradeoff is added complexity. The system includes a pump, coolant lines, a radiator or chiller, and sometimes a dedicated low-temperature circuit separate from the cabin air conditioning. Coolant does need periodic replacement. A common benchmark is a first change after one to two years or around 20,000 km, with subsequent replacements every two to four years or 40,000 to 80,000 km, though manufacturer recommendations vary by vehicle and climate.
Direct Refrigerant Cooling
Direct refrigerant cooling takes the air conditioning refrigerant already in the vehicle and routes it through cooling plates in the battery pack. In these systems, the refrigerant circulates directly through the cooling plate rather than chilling a secondary glycol loop first. This eliminates the middleman, so to speak, allowing the system to pull heat from cells more aggressively.
Because the refrigerant evaporates as it absorbs heat (a phase change), it can remove large amounts of thermal energy very quickly. This makes direct refrigerant systems especially effective during DC fast charging, when the battery generates the most heat in a short period. The complexity here is in system control: the refrigerant flow needs precise regulation so it doesn’t overcool some cells while leaving others too warm. Several newer EV platforms have adopted this approach to support higher charging speeds.
Immersion Cooling
Immersion cooling submerges battery cells directly in a non-conductive (dielectric) fluid. Because the fluid contacts every surface of the cell, heat transfer is more uniform than running coolant through channels pressed against one side. This approach also simplifies manufacturing since it doesn’t require the complex flow channels that indirect liquid cooling needs.
Several dielectric fluids are used or being tested. De-ionized water delivers the lowest maximum temperature rise. Engineered fluorinated fluids like Novec 7200 offer better temperature uniformity across cells and lower pressure drop, meaning the pump works less. Mineral oil is another option, though its higher viscosity demands more pumping energy compared to water-glycol systems.
Immersion cooling is still less common in mass-market vehicles than indirect liquid cooling, but it’s gaining traction for high-performance and high-capacity battery packs where keeping every cell at nearly the same temperature matters most for longevity and safety.
Phase Change Material Systems
Phase change materials (PCMs) represent a passive approach that stores heat rather than actively pumping it away. These materials, often wax-based or salt-based compounds, absorb large amounts of energy as they melt from solid to liquid. Packed around battery cells, they soak up heat spikes without any fans or pumps running.
The energy savings are notable. In one study simulating real driving conditions, a vehicle with a PCM-based system consumed about 15% less energy than one with air cooling and nearly 23% less than one with water-based cooling, because it didn’t need to power pumps or fans. Battery degradation was also slightly lower: about 6.95% capacity loss over 10 years, compared to 7.17% for air and 7.26% for water-based systems. The limitation is that PCMs can only absorb so much heat before they fully melt and stop buffering temperature. In sustained high-heat situations, they need to be paired with an active system to reject that stored heat.
Power Electronics Cooling
The battery isn’t the only component that needs cooling. The inverter, which converts the battery’s direct current into alternating current for the motor, generates substantial heat, especially during hard acceleration. DC-to-DC converters and onboard chargers also produce waste heat. These power electronics components typically use their own liquid-cooled plates, with coolant flowing through machined channels in the metal baseplate beneath the semiconductor chips.
In many EVs, the power electronics share a cooling loop with the battery pack, though some designs use a separate higher-temperature circuit. The cooling demands of modern silicon carbide (SiC) inverters are particularly intense, requiring careful engineering of coolant flow patterns to maintain uniform temperatures across the semiconductor modules during both steady driving and sudden bursts of acceleration.
Heat Pump Integration and Waste Heat Recovery
Most modern EVs tie their thermal management into a heat pump system that can move heat between components rather than simply dumping it. In cold weather, waste heat from the motor and power electronics can be captured through a heat exchanger placed in front of the heat pump’s condenser. This preheats the air entering the system, boosting heating efficiency and reducing the drain on the battery that cabin heating would otherwise cause.
This integration means the thermal system works in both directions. In summer, the same heat pump moves heat out of the battery and cabin. In winter, it scavenges heat from components that would otherwise waste it. The result is a unified thermal loop where cooling the drivetrain and heating the cabin aren’t separate energy costs but parts of one managed system. This is a significant shift from conventional cars, where engine waste heat provides “free” cabin heating. EVs have to be much more deliberate about where every unit of thermal energy goes.
How These Systems Compare
- Air cooling: Lowest cost and complexity, adequate for small battery packs and mild climates, but limited cooling capacity for fast charging or hot environments.
- Indirect liquid cooling: The current industry standard, offering strong thermal performance with moderate complexity and well-understood maintenance needs.
- Direct refrigerant cooling: Higher cooling capacity than indirect liquid, ideal for fast-charging support, but requires tighter system control.
- Immersion cooling: Best temperature uniformity across cells, simpler battery pack design, growing adoption for high-performance applications.
- Phase change materials: Zero energy consumption for thermal buffering, best paired with an active system for sustained heat loads.
Most production EVs today use indirect liquid cooling for the battery, liquid-cooled plates for power electronics, and a heat pump that ties everything together. Hybrids with smaller battery packs sometimes still use air cooling. As battery sizes grow and charging speeds increase, immersion cooling and direct refrigerant systems are becoming more common in newer designs.