How to tell whether your lithium batteries are a fire risk — and what to do if they are

We've heard a lot about how dangerous hot, fast-moving lithium battery fires are and their rising number — more than 1,500 in communities across Canada last year.

But most of us also keep and charge smartphones, power banks, e-bikes, vacuum cleaners, drills and lots of other lithium battery devices at home without any issues. 

So are all the fire warnings overblown? Are some kinds safer than others? Can batteries really go from safe to risky? What are the warning signs? And what should you be doing about this?

How safe are lithium batteries really?

Experts generally agree that overall, lithium batteries are very safe.

Vinny Gupta, assistant professor of fire safety engineering at the University of Waterloo, notes that more than 10 billion battery cells are now manufactured every year. "And we typically only hear about safety issues in just a few of them."

The problem is when the systems fail and they do catch fire, it's "quite dramatic," acknowledged Gupta, who does research that involves intentionally making them fail and catch fire to study their fire risk.

Safety measures typically built into consumer lithium batteries include temperature sensors, pressure relief valves to vent potentially flammable gases and systems to prevent overcharging.

So do you really need to take measures like watching them as they charge and unplugging them as soon as they're done charging, as firefighters advise?

WATCH | Regina fire chief offers tips on avoiding battery fires:

It's true that the battery should automatically stop charging. 

But experts note that a battery that has been safe all along can become a fire risk at some point.

How can a lithium battery that was safe become a fire risk?

David Giles, CEO of TempAlert, a Halifax company that sells heat-sensing battery-monitoring stickers, said even if people are using batteries as intended, they can become damaged and therefore hazardous.

That could be due to a defect. Or it could be due to an event, such as an e-bike or e-scooter collision.

He says that when you drop your phone, you may notice if you crack the screen. "But you also may have done other internal damage that might not show up right away" — including damaging the battery.

TempAlert makes heat-sensitive stickers that change from black to yellow at 60 C, indicating a problem with your battery. (TempAlert)

Heat, such as from charging your battery in the sun, can also cause damage.

Gupta said one of the most common ways to cause a battery to fail is by overcharging it. Typically, batteries are designed to prevent that, but some are more poorly designed than others, and the risk increases if they're tampered with or paired with the wrong charger.

Giles says that's easy to do, since most have connectors that fit into many devices. But he warns they may be designed for different voltages. The wrong charger "could be ramming, you know, 80, 90 volts into a battery only designed for 40. That's when you start having a major problem."

Repeatedly charging and recharging a battery over time can also eventually cause it to wear out and fail.

When that happens, does the battery catch on fire right away?

Here's the good news — usually no.

"Batteries don't just go into thermal runaway instantly," Giles said. Thermal runaway is a term for when a battery starts to rapidly self-heat, generating more heat and creating a feedback loop that can lead to a fire. "It progressively gets worse and worse."

Lithium batteries are found in many devices, including e-bikes, and most are safe. (Grant Linton/CBC)

When a battery first starts failing, it may feel hot to touch while charging — Gupta says that's "the earliest indication" that something is wrong. At that point, it will usually cool when you unplug it. 

Giles said that may happen repeatedly before it stays hot even after being unplugged.

So how much time do you really have before you have a dangerous fire? 

"To be honest, we don't really know," Gupta said, as it depends on what is going on inside the battery and the self-heating process is exponential once underway.

Giles said it could take days or weeks of charging and use, or it could take just 20 minutes.

WATCH | How do you put out a lithium battery fire?:

Are some kinds of lithium batteries less dangerous from a fire safety perspective?

The short answer is no. 

The two most popular lithium battery chemistries are NMC (nickel manganese cobalt) and LFP (lithium iron phosphate), which have different materials in their cathodes.

Several readers wrote in to suggest that LFP is less combustible and prone to overheating.

But in Gupta's opinion, "It's hard to really say if one chemistry is safer than [the] other … there are trade-offs."

It's true that LFP is less energy dense and goes into thermal runaway at a higher temperature (about 235 C, compared with 200 C for NMC). It also ejects fewer solid fragments of battery when overheated — but more gas, Gupta said: "And that gas is often laden with both toxic and flammable products."

So, how do you stay safe?

Buy batteries with Canadian safety certifications such as CSA, cUL, cETL on the charger. Make sure you use the correct charger with your battery, even if another one fits in the charging port.

These are the kinds of certification marks you should look for on your battery charger, according to the Government of Canada lithium-ion battery safety website. (Health Canada)

Keep an eye on your charging battery and its environment. Charge your device or battery on a hard, non-flammable surface (not on a couch or bed), where you can see it. Gupta recommends not putting the device in the path that you would need to use to escape in case of a fire incident.

Know the danger signs of a damaged battery.  They include feeling too hot, swelling, bad smells, gas or smoke. 

There are some devices that can help identify these signs, such as:

• TempAlert or other temperature-sensitive stickers that you can apply to the battery. 
• Heat detectors or alarms. Reader Adrian Hill of Crystal Beach, Ont., said he purchased one of these that he installed above the spot where he charges his e-bike. 
• A carbon monoxide detector. Gupta said many lithium batteries release carbon monoxide when overheated.

Know what to do if your battery overheats. Unplug it and get it to a safe, non-flammable place (such as outdoors, a sink or a bucket of sand) if possible. Don't try to charge it again, even if it cools, Giles says. 

This is Call2Recycle's kit for dealing with damaged, defective or recalled lithium batteries at hazardous waste facilities. (Call2Recycle)

If it cools down, you can take it to a technician or hazardous waste disposal site. Do not put it in the trash. Call2Recycle has more detailed information on dealing with damaged, defective and recalled batteries. 

If the battery continues getting hotter or releases gas or smoke, you're really in the danger zone.

"If you smell anything, that's bad," Gupta said. "You should leave and call the fire department."

Lithium batteries are around us everywhere and that's not going to change any time soon, he added. For the most part they're safe, but "it's important for people to be aware of the fact that they can fail and there are very simple things we can do that go a long way towards improving our personal safety."