Battery Cooling Tech Explained: Liquid vs Air Cooling Systems

Electric batteries must be kept within a narrow temperature range (typically about 20–40°C) for peak performance and safety. In fact, research shows Li-ion batteries live about 20 percent longer at 20°C vs 30°C, and life drops by about 40 percent at 40°C. Hot spots in a pack can trigger runaway and fires. Thus thermal management is critical. There are two main approaches: air cooling which uses fans or ambient air convection, and liquid cooling that employs circulation of a coolant through heat exchangers or plates in contact with the cells. Each has unique advantages and drawbacks depending on the application.

Air-Cooled Battery Systems

Air-cooled systems use ambient air flow – fans or natural convection – to carry heat away from the cells. They are simple and low-cost, since no coolant, plumbing or pumps are needed. Air cooling avoids leak hazards and extra weight of liquids. 

As a result, smaller or lower-power battery installations often rely on air-cooled designs. For example, many backup UPS batteries and small stationary packs use only room air conditioning to keep batteries cool. Advantages of air cooling include lower initial cost, simpler design, and minimal maintenance, thanks to no pump or liquid, simple fans or vents, lower cost, no coolant to leak, lighter systems. Good for low-power or well-ventilated packs

However, they are also marred with some limitations. Air has low heat capacity, so it removes heat slowly. Temperature distribution is less uniform and hot spots can form. Air cooling struggles at high power densities or in hot climates. For example, early EVs like the Nissan Leaf used air-cooled packs, but these designs showed safety issues under heavy use. Air systems also require larger surface area (heatsinks/fins) and may add fan noise and energy draw.

Thus, air cooling works best for small to moderate batteries or where cost is paramount. It is common in older EVs, like early Nissan Leaf, and simple UPS systems. However, it cannot efficiently support high charge/discharge rates or compact high-energy packs.

Liquid-Cooled Battery Systems

Liquid-cooled systems circulate a coolant, usually a water-glycol mixture or dielectric fluid, through tubes, cold plates, or jackets attached to the cells. This provides a much higher heat-transfer rate than the air counterpart.

Liquid coolants can absorb and transport heat far more effectively, ensuring uniform temperature across the pack and preventing hot spots. For example, a 2024 industry report notes that liquid cooling is extremely effective at dissipating large amounts of heat and maintaining uniform temperatures throughout the battery pack, thereby allowing designs that achieve higher energy density and safely support high C-rate applications.

Thus, the advantages of liquid cooling include excellent, high charge/discharge rates and fast charging. Further, it enhances efficiency and battery life and reduces risk of thermal runaway. In addition, liquid cooling can support very compact, high-energy packs that air cooling cannot. It is the preferred method in modern high-performance batteries.

Major battery makers like Tesla, BYD, and CATL use liquid cooling for EV and grid applications. Immersion cooling that involves submerging cells in dielectric fluid is an advanced form that eliminates hot spots entirely.

However, the complexity – requiring pumps, valves, and heat exchangers – and subsequent high costs are a limitation when compared to air cooling. Extra components also add up extra weight and parasitic power. Moreover, coolant circuits must be carefully sealed to avoid leaks. A 2024 analysis warns that liquid-cooling systems incur higher upfront costs and regular maintenance to prevent leaks. Furthermore, glycol coolant is toxic if leaked, so spill prevention and disposal are concerns. 

Batteries for EVs

In EVs, thermal management is paramount for safety, longevity and fast charging. Almost all high-performance and high-voltage EVs today use liquid cooling. As one industry review notes that liquid-based cooling for EV batteries is the technology of choice, which is rapidly taking over from forced-air cooling, as energy and power densities increase.

For instance, Tesla’s battery packs circulate a 50/50 ethylene glycol–water mix to cool cells. BYD’s LFP Blade batteries incorporate a liquid-cooling plate above each cell, giving a heat-exchange area much larger than a conventional pack and keeping temperature differences to about 1 °C.

CATL’s cell-to-pack (Qilin) design places coolant plates between cells, quadrupling heat-transfer area and halving thermal-management time. These liquid-cooled packs can safely deliver high currents and support fast charging providing “hot start” in 5 min and 10-minute fast charge.

Early or entry-level EVs used air cooling, but this is now rare. Nissan’s first-generation Leaf, for example, relied on ambient air flow. However, a 100 kWh battery can generate on the order of 5 kW of waste heat under heavy load, which requires more efficient liquid-cooling system. In practice, air-cooled EV packs are limited to very low-power use. By contrast, almost every modern BEV, such as Audi, Jaguar, BMW i and Kia/Hyundai, uses indirect liquid-cooling loops around the cells.

While liquid cooling enables rapid charging, tight packaging, and high power output, also reducing degradation in hot conditions, air-cooled EV batteries are simpler and cheaper but sacrifice performance.

Liquid Cooling for Grid-Scale Energy Storage

In utility-scale battery storage (BESS), thermal management is even more critical due to enormous capacity and power. Modern large installations , that is containerized Li-ion farms, almost universally use active liquid cooling. Large banks of cells generating many kilowatts of heat require coolant to maintain uniform temperature. 

While the most demanding thermal management applications, such as large-scale BESS, require active liquid cooling, smaller installations with low C-rate can be operated with air cooling.

Megawatt-scale projects by companies like Tesla (Megapack/Powerpack) and Sungrow use liquid-coolant loops through their modules. Tesla’s stationary products explicitly use a glycol-water mix for battery cooling. Sungrow’s PowerTitan 2.0 BESS is a fully liquid-cooled design, leveraging coolant throughout the rack to maximize efficiency.

Thus, in the context of grid-scale storage, liquid cooling allows very compact, high-density installations. It supports high C-rate (fast charge/discharge) for grid services like frequency regulation. It also enhances safety. For instance, liquid systems can rapidly quench developing hotspots and reduce fire risk.

Air cooling in grid BESS is generally limited to smaller or legacy systems. For example, low-power stationary batteries, such as home storage or small business UPS, may still use fan-cooled cabinets. But any multi-megawatt installation today will almost always incorporate liquid thermal loops to handle the heat load. A market report even forecasts the liquid-cooling market for stationary storage to grow rapidly from about USD 4 billion in 2024 to over USD 24 billion by 2033, driven by grid and EV demand.

Air Cooling for Data Centers: UPS and Battery Backup

Data centers primarily use batteries for UPS backup or short-term storage. In most cases the room’s air-conditioning suffices to keep batteries cool. 

Most data-center battery racks are essentially air-cooled by the existing HVAC system. The old standard air-cooled lead-acid backup already relied on ambient airflow. Now, even the lithium UPS is more tolerant of temperature. Indeed, UPS manufacturers often specify only standard operating-room cooling, that is around 20–25°C. In practice, banks of UPS modules may have fans or air channels, but dedicated liquid-cooling loops for batteries are uncommon.

Air Cooling or Liquid Cooling, Which is Suitable?

Ultimately, the choice depends on scale and requirements. Air cooling remains viable for low-C-rate or cost-sensitive systems like small BESS, legacy UPS, etc., while liquid cooling is the de facto solution for high-performance EVs and utility-scale storage. As battery technology advances (e.g. higher-power chemistries and solid-state batteries), effective thermal management – most often liquid or even advanced immersion cooling – will only become more critical.