BESS Thermal Runaway: Why Better Cells Alone Won’t Prevent It

What Is Thermal Runaway in a BESS?

Thermal runaway is the self-heating of an electrochemical system uncontrollably — the definition used by NFPA 855, the U.S. standard for stationary energy storage installations. It typically starts in a single cell, where an exothermic chain reaction releases heat and gas faster than the cell can dissipate them, driving temperature and pressure higher and potentially triggering neighboring cells.

Common triggers include:

• Overcharge or over-discharge
• Internal short circuits caused by manufacturing defects or cell aging
• Mechanical abuse, such as crush or puncture
• External heating or poor heat dissipation
• BMS failure or inadequate electrical protection

For utility-scale and C&I energy storage, the consequences go far beyond a single battery — fire, gas release, downtime, and reputational risk. That is why safety codes and test standards now treat thermal runaway as a system-level design consideration: NFPA 855 sets installation requirements for stationary energy storage systems, A

NSI/CAN/UL 9540 covers the safety of energy storage systems and equipment, and ANSI/CAN/UL 9540A provides the test method for evaluating thermal runaway fire propagation in battery energy storage systems.

Why “Better Cells” Alone Can’t Solve Thermal Runaway

Even with improved cell chemistry and stronger cell-level safety, heat still needs to be effectively managed at the system level. Thermal runaway is a system-level challenge involving:

• 🌡️ Heat generation & propagation
• 🌡️ Temperature uniformity
• 🔥 Hotspot control
• 💧 Cooling performance
• 🔍 Monitoring & system reliability

A safer cell reduces the probability of initiation — but it cannot absorb the heat released in a real failure, and it cannot stop propagation to neighboring cells. The system must be designed so that heat is removed quickly, temperatures stay uniform, and an abnormal cell is detected and contained before the event escalates.

Three Layers of Defense: Cell, Module and System

Effective BESS thermal safety is built in layers. Each layer answers a different question:

• Cell level — reduce the risk of initiation: cell design & chemistry, manufacturing consistency, electrical protection (BMS) and thermal uniformity.
• Module level — limit thermal propagation: thermal barriers/insulation, controlled venting and localized cooling.
• System level — contain the consequences: fire protection (detection & suppression), e-management (venting & relief), ventilation (gas exhaust) and thermal management (liquid cooling) for temperature control and uniformity.

A system that relies on any single layer alone — even the best cell — leaves critical gaps. Liquid cooling is one important layer: it continuously removes heat and keeps temperatures uniform, giving detection, suppression and venting systems the time they need to work.

Why Cold Plate Design Matters in Liquid-Cooled BESS

For liquid-cooled BESS, the cold plate is one of the key thermal interfaces between the battery cells and the cooling system. Its design directly influences:

• Heat removal
• Temperature uniformity
• Coolant flow distribution
• Pressure drop
• Weight, packaging and integration
• Long-term reliability

There is no single “best” cold plate design for every BESS application. Depending on the pack architecture and requirements, engineers may consider different solutions — including embedded tube, brazed, FSW, gun-drilled and micro-channel cold plates. Each option carries different trade-offs in thermal performance, manufacturing cost, weight, and long-term reliability.

Thermal Management Is About More Than Keeping the Battery Cool

Effective thermal management is not simply about keeping a battery cool. It is about how efficiently heat is removed, how uniformly temperature is maintained, and how reliably the system operates over time. In practice, that means:

• Lower maximum temperatures — less degradation and longer cycle life
• Smaller temperature differences — fewer hotspots and more consistent cell aging
• Stable operation — higher availability and lower total cost of ownership

For BESS owners and integrators, thermal management directly affects safety, performance, and project economics.

ALVC Custom Liquid Cold Plates for BESS

At ALVC, our focus is on the thermal management side — developing and manufacturing customized liquid cold plates for battery, energy storage, and power-electronics applications. Our cold plates combine optimized flow channel design with premium aluminum alloys for efficient heat dissipation, uniform temperature control, leak-proof structures, and long service life.

• ✅ Standard pack coverage — universal cold plates for 48S, 52S and 104S configurations
• ✅ Proven thermal uniformity — ±2℃ surface temperature difference with stamped & brazed series-parallel flow channel designs
• ✅ Manufacturing friendly — modular structure and one-step stamping with 99.5%+ brazing yield, ideal for mass production
• ✅ Fast time-to-market — prototype samples in 15 days, mass production delivery in 25 days, with 30,000 pieces/month capacity
• ✅ Customizable — mounting hole positions and dimensional tweaks tailored to your pack design

From prototype to mass production, our team partners with you to keep your BESS safe, reliable and competitive.

Ready to improve the thermal safety of your BESS? Contact ALVC for technical specs, samples, or a custom quote — we’re ready to support your project’s thermal management needs.

BESS Thermal Runaway FAQs

What causes thermal runaway in lithium-ion batteries?

Thermal runaway is usually triggered by overcharge, internal short circuit, mechanical damage, external heating or cell defects. Once started, the exothermic reaction generates heat and gas faster than the cell can release them, and the event can propagate to neighboring cells.

Can better battery cells prevent thermal runaway?

Better cells reduce the probability of initiation, but they cannot eliminate system-level risk. Heat propagation between cells and uneven temperature distribution must be addressed at the module and system level through thermal barriers, venting and effective cooling.

How does liquid cooling help prevent thermal runaway?

Liquid cooling removes heat directly from the cells and maintains temperature uniformity, reducing hotspots and thermal gradients. This slows cell degradation, lowers the risk of initiation, and gives monitoring and protection systems more time to respond.

What cold plate options does ALVC offer for BESS?

ALVC develops customized liquid cold plates, including stamped & brazed designs with series-parallel flow channels, as well as embedded tube, FSW, gun-drilled and micro-channel solutions, supporting standard pack configurations such as 48S, 52S, and 104S.

Which safety standards apply to BESS?

In North America, key references include NFPA 855 (Standard for the Installation of Stationary Energy Storage Systems), ANSI/CAN/UL 9540 (Standard for Safety of Energy Storage Systems and Equipment), and ANSI/CAN/UL 9540A (Test Method for Evaluating Thermal Runaway Fire Propagation in Battery Energy Storage Systems).

What do you see as the biggest thermal challenge for the next generation of BESS? Heat flux, temperature uniformity, coolant distribution, or thermal gradients? Share your thoughts with us.