E-bike batteries have made the news recently by bursting into flames. Don’t panic. Yours won’t – as long as you take some sensible precautions.

In another burnt-out room, on the page of another newspaper, there’s the charred and skeletal remains of another e-bike that spontaneously burst into flames. The number of e-bike and e-scooter fires has more than quadrupled in the UK since 2020. The London Fire Brigade has been called to one e-bike or e-scooter fire every two days so far in 2023. People have died.

It’s clearly a serious issue but it’s worth noting that the overwhelming majority of e-bikes are safe. That quadrupling came from a very small initial number. The fire incidents are newsworthy in part because they’re rare.

There’s also a sense in which the media is simply waking up to the potential risks of batteries. Unlike, say, petrol, we’ve all tended to assume that batteries are safe because they’re everywhere. Phones, laptops, toys, e-cigarettes – they all contain lithium-ion batteries. Any of these batteries can ignite. When they do, they burn fiercely and sometimes explosively, releasing toxic gasses and burning in a such a way that they’re hard to extinguish. It’s not a scenario unique to e-bikes, however. E-cigarettes have also recently made the news for causing fires in bin lorries.

When lithium-ion batteries fail catastrophically, they do so for one of several reasons.

• Overcharging. The battery is ‘cooked’ because the charger doesn’t stop charging it when its capacity is reached. The battery overheats and may ignite.
• Over-discharging. This isn’t the same as the battery displaying a 0% charge or zero bars. It’s your battery emptying beyond that point, beyond its depth of discharge limit. This damages the battery cells, which can subsequently overheat.
• Battery management system (BMS) fails. This is what controls charging and discharging rates. A functioning BMS will prevent overcharging and over-discharging. Yet some batteries don’t even have a BMS.
• Physical damage. Battery components are dislodged or fractured, which can cause a short circuit and a fire. This is what happens with e-cigarettes in bin lorries. With an e-bike, it could be an issue if you dropped the battery or crashed hard.

Look after your battery

The National Fire Chiefs Council (NFCC) has this to say about preventing e-bike battery fires. It’s important stuff that needs no journalistic gloss so we’re quoting the bullet points verbatim.

• Follow the manufacturer’s instructions when charging and always unplug your charger when it’s finished charging.

• Ensure you have working smoke alarms. If you charge or store your e-bike or e-scooter in a garage or kitchen ensure you install detection, we recommend heat alarms rather smoke detectors for these areas.

• Charge batteries whilst you are awake and alert so if a fire should occur you can respond quickly. Don’t leave batteries to charge while you are asleep or away from the home.

• Always use the manufacturer approved charger for the product, and if you spot any signs of wear and tear or damage buy an official replacement charger for your product from a reputable seller.

• Do not cover chargers or battery packs when charging as this could lead to overheating or even a fire.

• Do not charge batteries or store your e-bike or e-scooter near combustible or flammable materials.

• Do not overcharge your battery – check the manufacturer’s instructions for charge times.

• Do not overload socket outlets or use inappropriate extension leads (use uncoiled extensions and ensure the lead is suitably rated for what you are plugging in to it).

• In the event of an e-bike, e-scooter or lithium-ion battery fire – do not attempt to extinguish the fire. Get out, stay out, call 999.

The main takeaway is to get it right at the outset. Invest in good-quality e-bike from a brand you’ve heard of, and use only the battery and charger recommended by the manufacturer. This will cost more than an anonymous spare battery or charger found online. You’re buying certifiably safe electronics so it’s a cost worth paying. Don’t forget that you’ll save 25% or more on an e-bike or e-bike components anyway, simply by getting them through Cyclescheme.

When it comes to charging the battery, observe the other NFCC precautions. Don’t depend wholly on your memory or the battery management system for timings. Set a timer on your phone or, better yet, plug the charger into a timer switch. That way, even if the battery management system fails (extremely unlikely with a good-quality e-bike) you still won’t overcharge the battery.

There’s more to battery care than ensuring it doesn’t burst into flames, of course. You’ll also want to avoid it going flat mid-ride and to maximise its long-term lifespan. Cold is a problem here. Batteries don’t work well in the cold. You’ll notice this in winter because the range per charge will be lower – the outgoing charge from the battery having been reduced. What’s less obvious is that the incoming charge is also restricted. You can’t recharge a cold battery properly. If you try to do so, it won’t reach its full charge and its overall lifespan may be reduced.

For these purposes, ‘cold’ means less than about 5ºC. So if you park your e-bike in a chilly garage or shed over the winter, remove the battery and store it inside overnight. Recharge the battery indoors, too. You may still not get quite as far on frosty day but you’ll be maximising the available range (and battery lifespan).

Running the battery completely flat every few months can help it retain its maximum charging capacity. But you don’t need to do this on a daily or weekly basis. Topping up the battery each day is more convenient as you’re less likely to find yourself out of juice in the middle of a ride. Meanwhile, if you won’t be using your e-bike for an extended period, only partly charge the battery (Bosch recommends 30-60%) and store it like this.

Finally, don’t jet-wash the battery when cleaning your bike. Good-quality e-bikes have sufficient waterproofing to deal with downpours and puddles but high-pressure water is a different matter. Wash the bike by hand (bucket of water and a brush) if it’s dirty or has been ridden on salty winter roads. Leave the battery in place while you do this so the terminals aren’t exposed, then remove the battery so it and the bike can dry.