Quick answer: A lithium battery fire often gives warning first, though not always: a pack that is extremely hot, swells or leaks, hisses or cracks, or gives off a strong, strange smell. Turn the charger off and pull its plug, and move the battery outdoors if you can do it carefully. Smoke means everyone out and a call to 999.
Why does a lithium battery catch fire?
A battery pack is a block of lithium-ion cells packed tightly together. When one cell gets hot enough, chemical reactions inside it start making heat faster than it can escape. The statutory guidelines for e-bike batteries call this thermal runaway: the cell gives off gas, its casing can burst, and the gases released can be flammable and toxic. Heat then passes to neighbouring cells, so the failure runs through the pack and can become a fire that grows very fast.
The government lists what makes this more likely: packs that are damaged, counterfeit, badly made or outside safety rules, a charger that does not match, and repairs or changes made with incompatible parts. That list is the same whether the pack powers a bike, a board or an e-scooter made for rough ground.
What are the warning signs before a lithium battery fire?
Not every fire gives notice; some start without any. Many do, though, and your senses can pick the signs up whenever a pack is charging or has just been used:
| Sense | Warning sign | What it tells you |
|---|---|---|
| Touch | Much hotter than usual, too hot to hold | Some warmth while charging or riding is normal. Extreme heat can mean a defect, and the DfT says to stop charging straight away. |
| Sight | The case bulges, swells out of shape, shows a lump or leaks | Swelling is a frequent mark of a failing battery. |
| Hearing | Hissing or cracking from the pack | Failing lithium batteries have been reported to make these sounds. |
| Smell | A strong smell, or one you cannot place | A failing battery is one possible cause, and the fumes may be toxic. |
| Behaviour | It no longer fills completely, or charging takes longer than before | A slower warning, but one the DfT lists as well. |
| Smoke | Any smoke from the pack or the vehicle | A fire has already started. Stop checking and leave. |
When do you stop checking and leave the room?
The moment you see smoke. A lithium battery fire can spread quickly and is very hard to put out, so OPSS advice is never to fight one yourself. Leave the room, then the building, as fast as you can, and dial 999. Raise the alarm on your way so everyone else leaves too, and do not go back for the vehicle or anything else.
What happens after you spot a warning sign?
If there is no smoke yet, the DfT's advice comes down to three steps:
- Turn the charger off at once and pull its plug.
- If you can manage it carefully, move the battery, or the vehicle with the battery inside, outdoors. Leave it where people and animals cannot get near it, with nothing close by that can catch fire.
- Do not charge it, use it or bring it back inside. Ask its maker or the retailer for instructions, or look up how to dispose of it.
Once it is over and nobody is in danger, report the faulty battery. Citizens Advice covers England and Wales, Advice Direct Scotland covers Scotland, and the maker or retailer should hear about it too.
How do the warning signs show on each vehicle?
E-scooters. The pack usually sits under the deck or inside the stem, so swelling can show as a deck that bulges or a cover that no longer sits flat. The DfT notes that fire services have reported a significant number of battery fires involving privately owned e-scooters, so the charging habits further down apply in full.
E-bikes. A removable pack is easy to inspect off the frame, so look at the case and the contacts each time it goes on charge. Most of what prevents an e-bike battery fire happens at the charger: our guide to setting up a charging spot for an e-bike covers it, and our page on adult e-bikes and what to check helps with the choice of bike.
Electric skateboards. The battery sits in an enclosure under the deck, where hard landings and stones can crack it. Turn the board over and look underneath, especially on mountain boards and other off-road decks.
Electric unicycles. The battery is inside the shell next to the wheel, so a fall can damage it without leaving a mark. After any heavy fall, treat the pack on single-wheel boards and unicycles as suspect until someone competent has looked at it.
Hoverboards. The pack is built into the casing. For the hoverboards we sell, our guide to caring for a hoverboard battery goes through the checks.
Lithium battery safety: how do you lower the risk?
- Know your seller. OPSS advises buying from sellers you trust, and checking that they explain how the product meets UK safety law.
- Keep the right charger. Use only the charger designed for that battery, or a substitute from its maker.
- Charge where you can react. Charge only when you are up and nearby, with nothing over the pack and away from exits, and disconnect once it is full.
- Store it with care. Where a pack rests matters as much as where it charges; see where to keep a battery between rides.
- Leave the pack alone. No modifications and no home repairs. Repairs go to a professional, using parts the maker recommends.
- Register it with the maker. The DfT points out that a registered product lets the maker reach you about recalls and safety alerts.
Act on these signs
Smoke means it is already burning: alert everyone, leave and dial 999 once outside. With no smoke yet, turn the charger off, pull its plug, keep the battery out of use and tell the manufacturer or the retailer if:
- the pack is far hotter than normal to the touch;
- it has bulged, swollen, cracked or begun to leak;
- hissing or cracking sounds come from it;
- there is a strong or unfamiliar smell around it.
It is illegal to ride a privately owned e-scooter on roads, pavements or cycle lanes, or in parks. Ride it only on private land, with the landowner's permission.
Questions riders ask
Can a lithium battery catch fire when it is not charging?
Yes. Most advice focuses on charging, but the DfT warns that a damaged pack can catch fire rapidly and without warning, and asks riders to watch for the signs while riding as well. That is why where a pack is stored matters too.
Should I keep a fire extinguisher for an e-bike or scooter battery?
Do not plan to fight the fire. OPSS advice is that nobody should tackle a lithium-ion battery fire themselves: leave the area or the building as quickly as possible and call 999. A working alarm near where batteries are kept is the more useful kit.
Where do I report a battery that overheated or caught fire?
Citizens Advice takes reports for England and Wales, and Advice Direct Scotland for Scotland; tell the maker or retailer as well. The DfT suggests reporting once the incident is over and nobody is in danger.
Which alarm suits a room where batteries are kept?
For garages and kitchens, fire services prefer heat alarms to smoke alarms; elsewhere the DfT advises working smoke alarms. Either way, fit one wherever batteries are charged or stored indoors, and press its test button regularly.