Have you ever noticed that, after prolonged use, the batteries of some electronic devices can swell, overheat, and even catch fire—occasionally, we even see reports online of electric vehicles or smartphones bursting into flames? Behind these incidents lies a common factor: the battery’s inherent “fire‑resistance.”

Today, let’s talk about lithium batteries. Fire resistance rating — A concept that sounds highly technical but is, in fact, closely tied to everyone’s safety.

Don’t get it confused—“fire‑proof” in the context of lithium batteries has more than one meaning.

Many people assume that a battery’s fire‑safety rating simply means “the battery itself won’t catch fire.” In fact, that’s not the case.

Fire safety for lithium batteries is like a set of… Layer upon layer of defensive armor : At the innermost layer is the flame-retardant performance of the battery‑cell materials; in the middle lies the safety design of the battery module itself; and on the outermost layer is the fire‑protection strategy for the entire energy‑storage system.

Simply put: From a single battery cell, to a battery pack, and then to an energy storage power station. Each floor has its own distinct “fire‑safety examination” and rating criteria.

Layer 1: Component Materials — Can a plastic housing extinguish itself?

Imagine the battery casing as a fireproof suit worn by a person. If the suit itself is vulnerable to fire, no matter how skilled the person inside may be, it won’t make a difference.

The most commonly used standard for evaluating a material’s flame-retardant performance is UL 94 You can think of it as a “plastic flammability test,” with ratings ranging from low to high roughly as follows:

HB : Burns relatively slowly; just passable.

V-2 : The flame can be extinguished within 30 seconds, but burning plastic droplets will fall (which may ignite other materials).

V-1 : Extinguishes within 30 seconds, with no burning drips or debris falling.

V-0： Extinguishes within 10 seconds , no burning drips — this is a fundamental requirement for the casings and supports of most lithium batteries.

5VA / 5VB : Even more stringent—samples must withstand five burn cycles without being easily burned through—intended for high-performance or large-scale energy storage batteries.

Also, there is... VTM-0 , specifically for the battery inside Plastic film (For example, insulating films and labels) are tested, and the standard is equivalent to V‑0.

In a nutshell: High‑quality battery plastic components must self‑extinguish upon removal from the flame.

Layer 2: Cells and Modules — Could They “Burst” Under Extreme Conditions?

Fire resistance of the materials is fundamental, but the battery’s intrinsic “safety DNA” is even more critical. In the event of an internal short circuit, mechanical compression, or even puncture by a sharp object, will it immediately catch fire or explode?

There are two heavyweight certifications here: UL 1642 and UL 1973 。

UL 1642 It is an “entry-level certificate” at the cell level. It will use A flame of about 800°C Directly expose the battery cell to flame for 10 seconds. After removing the ignition source, the cell must self‑extinguish and must not explode. If it fails this test, it cannot be brought to market under any circumstances.

UL 1973 This standard is even more stringent, applying to the entire battery module—for example, residential energy storage batteries or elevator backup power supplies. It not only mandates cell‑level safety but also imposes additional requirements on the battery management system and thermal‑management design. In certain components, the flame‑retardant rating must reach as high as 5VA。

You can think of it this way:
UL 1642 It means “the battery cell must not behave erratically on its own.”
UL 1973 “It means that even in the event of an accident, the entire battery system must remain under control.”

Layer 3: System Level — In the event of a fire, how can we prevent it from spreading uncontrollably?

At this stage, the concern is no longer “whether a fire will break out,” but rather… If a single battery cell were to experience thermal runaway, could the fire spread throughout the entire energy storage facility?

Here, it’s worth mentioning a recent development: Lithium battery fires have been classified as a separate category. 。

In the past, fires were classified as Class A (solids), Class B (liquids), Class C (gases), Class D (metals), and so on. However, lithium‑battery fires are quite unique: Extremely high fever, capable of triggering a chain reaction, releases toxic and flammable gases, and is prone to reignition. . Therefore, international standards BS ISO 3941:2026 A new category has been specially added —— Class L fire , which is used to define lithium battery fires.

This means: You can’t use the old methods to fight it. , requires specialized fire suppression systems and strategies.

In addition, there is another important test for energy storage systems called UL 9540A It’s not about how “fire‑proof” the battery is, but rather… Artificially inducing thermal runaway in a battery cell Then, observe whether the fire can be contained within the module and prevented from spreading to adjacent units. The outcome of this test directly determines whether the energy storage station can be located next to residential buildings and whether a fire‑break wall is required.

Chinese standards are no less advanced either.

In China, lithium batteries used in electric vehicles must comply with GB 38031 Standard. The latest 2025 edition has been upgraded from “ensuring a 5-minute escape time” to The battery system must not catch fire or explode. 。
Meanwhile, the lithium batteries used in portable electronic devices (such as smartphones and laptops) must meet GB 31241 The requirements.

You see, fire‑safety requirements are becoming increasingly stringent; it’s no longer enough to simply “be able to escape once a fire breaks out”—the goal is now to “prevent fires from breaking out in the first place.”

To sum up, don’t let yourself be fooled anymore.

Lithium battery fire protection rating = three-layer protection system

For the average consumer, you don’t need to memorize these numbers, but you can remember three key points:

For lithium batteries from reputable brands, the casing and plastic components must meet the V‑0 flame‑retardant rating, which requires that the material self‑extinguishes upon removal from the flame.

The more comprehensive the safety certifications a battery has—such as UL 1973 or GB 38031—the less likely it is to experience incidents.

Do not modify, puncture, or expose the battery to high temperatures without authorization—no matter how high the fire‑resistance rating, it cannot withstand deliberate sabotage.

Finally, if your phone, electric scooter, or power bank frequently… Severe fever, swelling, and a sharp drop in battery life In that case, the internal resistance has likely increased (remember what we discussed earlier about internal resistance?), meaning the battery has already aged. At this point, don’t hesitate to replace it. Safety always comes first. 。