Article · Origin and cause
Did the Battery Start the Fire, or Was It Caught in It?
Dustin Herte, CFEI | Energy Forensics Group
A fire damages a garage containing an e-bike, cordless tools, and several battery chargers. During the examination, investigators recover a ruptured battery pack and scattered cells. Someone describes the loss as a “battery fire.”
That description may be accurate, but it leaves an important question unanswered: when did the battery become involved?
A battery can initiate a fire. It can also fail after heat from another source reaches it. In either situation, investigators may find cells that vented, ruptured, or entered thermal runaway. Establishing what happened to the battery is part of the investigation. Establishing where that event falls in the sequence is what connects the battery evidence to the origin and cause of the loss.
For an attorney or adjuster reviewing the file, that distinction deserves attention before the discussion turns to defects, misuse, or responsibility.
External heating can drive lithium-ion cells into thermal runaway. In controlled experiments, UL Research Institutes’ Fire Safety Research Institute induced thermal runaway in e-scooter battery packs through both external heating and intentional overcharging. Both methods produced propagation through the tested packs, flaming combustion, and damage to their enclosures. Those experiments demonstrate why evidence of a battery’s energetic failure does not, by itself, identify the event that initiated it. FSRI’s battery experiments.
A battery exposed to an existing fire may subsequently contribute to its growth. Its involvement can be substantial even when it was not the initial source. An investigation therefore needs to address both the ignition sequence and any later contribution by the battery.
Consider the difference between two witness accounts:
“I saw smoke coming from the battery before anything else was burning.”
“I heard popping from the garage and then saw the battery burning.”
Both accounts deserve investigation. They provide different information. The second account leaves open what was happening before the witness noticed the battery. The first is more specific about the observed sequence, but still requires examination of visibility, timing, and other available evidence.
The investigator needs to separate what a witness actually observed from the explanation the witness formed afterward.
Early photographs, security-camera recordings, and observations from responding firefighters may help establish that sequence. Their value depends partly on when they were recorded and what they show. A video beginning after flames have spread through the room cannot establish the first item ignited merely because a battery is visible in the footage.
This is why scene documentation matters alongside the recovered components. The National Institute of Justice’s fire-scene guidance emphasizes witness identification, systematic photography, and documentation of evidence locations before collection. A battery examined in a laboratory should remain connected to that scene record. NIJ’s fire-scene investigation guide.
The distribution of damage also requires context. A heavily damaged area can attract immediate attention, particularly when it contains recognizable battery debris. But fire patterns develop as the fire grows. Ventilation and the arrangement of combustible materials affect that development. FSRI’s full-scale research specifically examines how ventilation influences fire patterns and electrical-system damage. The resulting patterns must be interpreted against the conditions that produced them. FSRI’s fire investigation research.
For the garage example, the examination should account for the battery’s original location, nearby materials, other potential ignition sources, and changes to the scene during suppression and overhaul. A close photograph of a ruptured cell cannot supply that information.
Laboratory examination can then address more specific questions about the recovered battery.
Depending on the condition of the evidence, radiography and computed tomography may document internal arrangements and damage before the component is opened. In its investigation of the 2013 Boeing 787 battery incident in Boston, the National Transportation Safety Board used CT scans and digital radiography to examine the batteries and cells for damage and other anomalies. The scans documented distorted cells and displaced internal components. NTSB interim factual report.
An image still requires interpretation. If examination reveals internal damage, the investigator must address whether it preceded the fire or resulted from the battery’s subsequent exposure and failure. The fact that a condition is visible does not establish when it developed.
The same care applies to an internal short circuit. Identifying a short does not automatically establish a manufacturing defect. The proposed explanation must account for how the short developed and whether the evidence supports that sequence.
Comparison with an undamaged example of the same product can help identify departures from its original construction. Product documentation and charging specifications may also inform the analysis. Each finding should be tied to a specific question rather than presented as a collection of technical observations that appears persuasive simply because it is detailed.
There are also limits to how far the evidence can take an investigation.
A battery’s response to heat depends on its characteristics and condition. Research published through NIST found different thermal behavior among the commercial cell types tested under external heating. Findings from one cell design or test condition should not become a universal rule about how every battery will look after a fire. Research on external heating and battery failure.
An investigator may be able to establish that a pack experienced thermal runaway while remaining unable to determine what initiated it. In another case, the evidence may support an origin within the battery system but leave the precise failure mechanism unresolved. Those are different levels of knowledge, and the report should distinguish them.
The practical question for counsel is whether the report explains the steps between observation and opinion. A photograph of damaged cells, followed by a conclusion that the battery caused the fire, leaves those steps missing.
When reviewing a battery-fire investigation, useful questions include:
- What evidence establishes the area of origin, and where was the battery within that area?
- What is known about the sequence before the battery became visibly involved?
- How was external heating evaluated as a possible trigger?
- Which findings help distinguish pre-existing damage from damage produced during the fire?
- What alternative explanations were tested, and what evidence supports rejecting them?
- Which conclusions remain unresolved because evidence is missing or inconclusive?
These questions apply equally when evaluating your own expert’s work or reviewing another party’s report. They help identify whether further examination could resolve a specific issue and whether the current opinion goes further than the evidence permits.
For a new loss, preserve the opportunity to answer them. Arrange for qualified personnel to document and recover relevant evidence, retain available recordings in their original form, and coordinate examination before components are altered. A battery delivered to the laboratory without its location, surrounding scene, or event history may leave questions that even a careful teardown cannot answer.