Crash damage could be the biggest problem for bona fide e-bikes

E-bike fires increased by a massive 78% last year compared with 2022, according to the latest data from the London Fire Brigade (LFB), which has launched its #ChargeSafe campaign to try and control the problem.

The capital saw 155 e-bike fires last year, and 28 e-scooter fires, while combustion of lithium-ion batteries from bikes is now the fastest growing cause of fire. Batteries and motors that do not meet UK safety standards are to blame, according to the LFB. 

Are e-bike mountain bikes on the hook then? Almost certainly not, we’re pleased to say, because the best electric mountain bikes have built in failsafes to minimise the chances of them burning up. It’s the counterfeit batteries or cheap conversion kits bought from online marketplaces that are to blame, according to the LFB.

However, having a big battery pack stashed in your house is statistically going to increase the chances of a fire. That’s because faulty or damaged batteries are at greater risk of setting alight, and mountain biking does put batteries in harm’s way. Accidentally using the wrong charger is potentially dangerous too. 

E-bike safety need to know, from the London Fire Brigade

  • Store your bike in an external location, ideally a shed, garage or outbuilding. If that’s not possible, keep it out of thoroughfares and hallways
  • Use the correct charger to avoid an increased risk of fire. This is because different motors require different voltages
  • Don’t convert your analogue bike into an e-bike with a DIY kit… although that’s probably a given for proper mountain bikers
  • Check your battery and charger both meet UK safety standards – look for the UKCA or CE mark that ensures that the products meet UK and EU safety, health or environmental requirements
  • Check for signs of malfunction – it could be hot to the touch or have changed shape

What’s inside an e-bike battery

Lithium-ion batteries are made up of rows of cells, packed into a tough and inflexible casing. There’s also a Battery Management System (BMS) or perhaps multiple BMSs taking care of groups of cells, and this is the important bit to a quality battery.

The BMS controls how the battery discharges when you ride, it’s the software that tells the battery how many watts to put out, when to go into limp mode and when to shut down. If there’s an error it’ll communicate that to your display too. 

Without a BMS (there are plenty without them) you can discharge a battery too much, or overcharge it too, which leads to a chemical imbalance and potentially a fire. This can also lead to something called thermal runaway, a cell overheats and leads to a chemical reaction that in turn overheats the next cell, and so on.

How to look after your battery

If you’re riding a bike from a reputable brand and plugging it into the proper charger then you can rest easy about the BMS. But there is one more way a battery can fail, and that’s mechanical – you and crash and damage it. This means you need to inspect your battery regularly. And, just to be on the safe side, don’t leave the bike plugged in and charging overnight.