Lithium-Ion Batteries: Recognising Fire Risks and Responding Safely
Lithium-ion batteries are used in smartphones, tools, e-bikes, laptops and many other devices. Intact, high-quality products are generally safe when used as intended. A battery becomes hazardous if it is damaged, overheated, used with an unsuitable charger or kept in use despite clear warning signs. This can lead to thermal runaway: the cells heat up independently, release flammable and harmful gases and may catch fire very quickly.
A clear, dry charging area, suitable chargers and supervision significantly reduce the risk. Image note: AI-generated illustration.
The short answer: how dangerous are lithium-ion batteries?
If a battery becomes unusually hot, swells, hisses, crackles, emits a pungent smell or smokes, keep your distance, warn others and call 112 immediately if there is smoke or fire. Do not inhale smoke or vapours.
An undamaged battery used correctly does not normally present an immediate fire risk. Mechanical damage, unsuitable or defective chargers, overcharging, deep discharge, high temperatures and internal short circuits increase the risk. Poor-quality cells or a faulty battery management system can also be factors.
When self-reinforcing heating occurs inside a battery, specialists refer to thermal runaway. Hot, toxic, corrosive and flammable gases and particles may then be released. The course of such an event is difficult for non-specialists to predict, and the battery can reignite after it appears to have settled.
Warning signs: when a battery must be taken out of service immediately
Inspect the battery, casing, connections and charger regularly, especially after a fall, impact or contact with water. A damaged casing is not merely a cosmetic defect. Cells may be crushed internally or electrical safety functions impaired even if there is no visible flame.
Stop charging only if you can do so without putting yourself at risk. Do not touch, open, compress or test-charge a battery that is hot, swollen, leaking or smoking. Isolate the area and obtain specialist assistance. If there is smoke, hissing, a strong smell or rapid heating, everyone must leave the area and call the fire brigade.
unusually high temperature while charging or at rest
swelling, deformation, cracks or a loose casing
a pungent or chemical smell
hissing, crackling, unusual noises or leaking substances
smoke, discolouration or melting on the battery or charger
a noticeably shorter run time combined with unusual heating
Swelling, cracks and deformation are clear warning signs. Do not continue charging or using the battery, and arrange safe disposal. Image note: AI-generated illustration.
Charging lithium-ion batteries safely
Use only the charger supplied by the manufacturer or one that the manufacturer has expressly approved. The voltage, charging current and communication between battery and charger must be compatible. A plug that fits mechanically does not prove technical suitability.
Charge on a stable, dry and non-combustible surface with good air circulation. Paper, cardboard, textiles, aerosols and other combustible items must not be kept nearby. Do not cover the charger or battery. The German Environment Agency also recommends a charging area close to a smoke or fire detector and supervision while charging.
check the charger and cable for damage before use
allow the battery to reach room temperature before charging
do not charge on a bed, sofa, carpet or among cardboard boxes
keep ventilation openings clear and do not cover the charger
supervise charging where possible and do not leave it running while you sleep
disconnect a fully charged battery from the charger as instructed by the manufacturer
Do not simply resume charging after a fall, impact or contact with water
An e-bike, power-tool or laptop battery may look almost undamaged even though cells or protective circuits inside have been stressed. Do not automatically recharge a battery after a serious fall, accident, crushing incident or water ingress. Follow the manufacturer’s instructions and, if in doubt, have the product assessed by an authorised specialist.
Do not open or repair battery packs yourself. Individual cells can deliver high currents, and metal tools, jewellery or loose contacts can cause short circuits. Even an apparently simple cell replacement alters the tested system comprising cells, casing, temperature monitoring and battery management.
Storing and transporting batteries correctly
Store batteries somewhere dry, protected from direct sunlight and within the temperature range specified by the manufacturer. A hot vehicle, proximity to radiators and freezing conditions are unsuitable. Terminals and contacts must not touch coins, keys, screws or other conductive objects.
The suitable state of charge and inspection intervals for longer-term storage depend on the product and manufacturer. Avoid both permanent full charge and deep discharge unless the instructions state otherwise. Batteries must be protected against movement, impact and short circuits during transport. Additional dangerous-goods requirements may apply to larger or commercial shipments.
Managing lithium-ion batteries in the workplace
Organisations should record which batteries are present, where they are charged and what quantities are stored at the same time. Charging areas must not be located on escape and rescue routes. The type, number, energy content, spatial conditions and potential consequential damage form part of the risk assessment. This determines suitable separation, detection, instruction and emergency measures.
Employees need clear rules for approving charging, visual inspections, damaged batteries, exclusion zones and raising the alarm. These topics belong in workplace fire safety instruction. Training fire safety assistants complements these arrangements, but it does not replace safe charging areas or technical protective measures.
specify approved combinations of batteries and chargers
define charging locations and maximum quantities
exclude escape routes, stairwells and areas with a fire hazard
identify and separate damaged batteries and arrange specialist handling
provide regular instruction on warning signs and alarm procedures
document measures derived from the risk assessment
Disposing of defective batteries correctly
Lithium-ion batteries must never be placed in household waste, general waste bins or scrap metal. They can start fires in collection and sorting facilities. Take used batteries to an approved return or collection point and follow its acceptance conditions.
For small used batteries that are cool and externally undamaged, cover exposed terminals to prevent a short circuit. Do not transport a damaged, swollen, leaking or unusually warm battery without first obtaining advice. Inform the collection point of its condition in advance and follow its instructions. Never open, puncture or force a battery into an arbitrary airtight container.
What should you do if a battery smokes or burns?
Do not experiment. Do not carry a smoking battery, cover it with blankets, open it or move it to another room. Call the fire brigade and state that a lithium-ion battery is involved.
Warn others, leave the danger area and close the door if possible without putting yourself at risk. Call 112 from a safe distance and explicitly report a burning or smoking lithium-ion battery. Keep your distance and avoid smoke and escaping vapours.
Burning lithium-ion batteries can react unpredictably. At a workplace, extinguishing measures may be taken only in accordance with the risk assessment, emergency plan and training. The DGUV states that trained fire safety assistants and defined measures are required. Personal safety and a clear escape route take priority. The article Extinguishing an Incipient-Stage Fire: When to Act and When Not To explains these limits for intervention.
Checklist for home and the workplace
The following points provide a short charging-area check. Organisations should supplement them with their risk assessment, assigned responsibilities and documented emergency measures. The guide Fire Extinguishers in the Workplace: Which Ones Does My Organisation Need? explains which fire extinguishers are generally required at a site.
battery, charger and cable are undamaged and compatible
charging area is dry, clear, non-combustible and ventilated
no combustible items or escape routes are in the immediate vicinity
charging is not left running overnight or unattended
battery is protected against heat, freezing, impact and moisture
everyone involved knows the warning signs, isolation procedure and alarm route
used and defective batteries are not placed in household or general waste
in the event of smoke or fire: keep your distance, evacuate and call 112
Frequently asked questions
Can a lithium-ion battery catch fire without warning?
Technical defects can remain unnoticed. However, warning signs often include unusual heating, swelling, odours, noises or smoke. Damaged or abnormal batteries must not be used or charged again.
Can you charge a battery overnight?
Charging should be supervised where possible. Charging while you sleep makes it harder to react quickly to heat, odours or smoke. The manufacturer’s instructions remain decisive. A clear, non-combustible charging area and a suitable smoke alarm provide additional protection.
What should you do with a swollen phone or laptop battery?
Do not continue charging the device, press or remove the battery. Keep your distance. If there is heat, an odour, noise or smoke, leave the area and call 112. Otherwise, ask the manufacturer, a specialist company or a collection point how to proceed safely.
Which charger is correct for a lithium-ion battery?
Use the original charger or one expressly approved by the manufacturer for the battery and device. A matching plug alone says nothing about the voltage, charging current or safety communication.
Can lithium-ion batteries go in household waste?
No. Used batteries must be taken to a suitable return or collection point. If a battery is damaged, swollen, leaking or warm, inform the collection point of its condition before transporting it.
Sources and technical basis
Create clear procedures from the charging area to a fire emergency
Manage battery risks safely in the workplace
Practice-based fire safety instruction and trained fire safety assistants connect technical prevention with safe behaviour during an incident.
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