Are Electric Bikes Safe?

What Is An Ebike?

With Ebike and E-Scooter fire safety hitting the headlines in a sensational way recently you’d be forgiven for thinking that all Electric Bikes are potentially dangerous. That is simply not the case therefore let us walk you through what an electric bike is and what makes them safe and unsafe.

We have never had a report from any of our customers that their battery has malfunctioned in a way that could cause a fire.

Electrically Assisted Pedal Cycles (EAPC’s)

Road-legal EAPC’s sold as complete Ebikes are typically sold through reputable UK retailers like ourselves. These are the only types of bikes that we sell. They are safe and we have never had a fire.

The bikes we sell feature Bosch, Yamaha or Ebikemotion systems. They have undergone thousands of hours of product development and testing. They are safe to handle, use and store.

A UK legal electric Bike is classed as an “Electrically Assisted Pedal Cycle” (EAPC). It is legal to sell and use in the UK just like a normal bike if it typically meets the following criteria:

  • The bike must has pedals to propel it.
  • An EAPC must show the manufacturer of the motor or its power output.
  • It must also show the battery voltage or maximum speed.
  • An EAPC’s motor must have a maximum power output of 250 watts.
  • It must not propel the bike more than 15.5mph or 25 km/h under motor assistance.
  • A throttle is allowed up to walking pace (3-4mph)

We only sell EAPC bikes that have been fully tested and certified to EN15194 standards.

E-Mopeds & E-Motorbikes

Unregistered e-mopeds and e-motorbikes are often misreported in the media as ebikes or electric bikes. They typically travel at much faster assisted speeds than 15.5mph and have a throttle. Riders don’t normally have to pedal.

Any electric bike that does not conform to EAPC regulations is classed as a motorcycle or moped. It must be taxed, insured and registered. Riders must have a valid driving licence, insurance and wear a helmet to operate one legally in the UK.

Electric Bike Conversion Kits

Powered bikes created from kits are often purchased via online marketplaces. These will often fail EAPC regulations and make riding them illegal. There is a high risk of battery malfunction and fire with these products as the components may not be compatible. They could be poorly made and are cheaply mass produced. 

The types of bikes and kit pictured below are not EAPC E-Bikes in the UK

electric motorbike
electric bike conversion kit

Are E-Bike batteries safe?

E-Bikes are typically fitted with Li-on batteries which can also be found in other rechargeable devices.

According to UK insurer Zurich, 167 fires were reported to local fire departments in the UK during 2022. The primary cause was a li-on battery in an electric scooter or bike. It’s estimated that there are over one million privately-owned electric scooters (illegal if used in the public domain) and over half a million electric bikes. That means just 0.011% set on fire last year with the vast majority belonging to eScooters.

Safety warning – Never open any lithium-ion battery pack. They’re not designed to be serviced and opening them is a safety risk.

Your lithium-ion eBike battery isn’t just one big battery in a case. It is actually made up of lots of much smaller ‘cells’. The cells are connected as circuits to a Battery Management System (BMS).

The differences between major brand and cheap batteries:

Let’s look at the differences between batteries produced for mainstream manufacturers of eBike systems. Bosch, Shimano, Yamaha etc. and what you might expect to find (or not) inside cheaper, poorly manufactured eBike batteries.

Yamaha, Bosch, Shimano and other top manufacturers…

It might come as a surprise that none of the top Ebike manufacturers make their own batteries.

For example, inside a 630Wh battery on a Haibike FLYON eBike, you’ll find cells made by Murata Manufacturing Co Ltd. They are the principal cell manufacturer for Sony too. These cells are used by another German company called BMZ Group to build the battery. Then the complete unit is sent back to Haibike for use on their production line when building the eBike.

Bosch make safe ebike batteries
Yamaha Ebike Systems Logo
Shimano Steps Ebike Logo

Why don’t they do it themselves? Safety.

Using properly accredited battery pack manufacturers guarantees an exceptional level of engineering design and safety. Bicycle manufacturers are not Li-on battery experts. They know what they need but that doesn’t mean they’re the best people to do it. Like other industries using Li-on battery packs in their products, bicycle manufacturers sub-contract this work out. They are internationally accredited manufacturers with world renowned test laboratory facilities. If you need an expert job done, it makes absolute sense to get an expert to do it for you.

As well as very well built, safe and tested batteries, these firms also supply directly compatible and accredited charging solutions. Given that most Li-ion battery fires start while the product is on charge, this is an overlooked aspect of battery safety.

“Unbranded” manufacturers

At the opposite end of the market are cheaper Far Eastern manufactured batteries and worse still, the DIY market.

Unbranded batteries are almost exclusively from the Far East. Assembly is closer to the cell production factories and where materials/labour is cheaper. These appear later with lots of different brands on them.

These are quite often reasonable quality. They have a good BMS and internal connections, but in order to keep prices low they are made with cells from smaller (normally Chinese) cell manufacturers (i.e. not Sony, Samsung, Panasonic, LG, etc). These typically don’t perform as well and have much lower cycle count (the number of times they can be charged before they start to degrade). Often the performance characteristics are falsely inflated and as a result they sometimes don’t provide the level of capacity (range) advertised and also have a much shorter shelf life.

Some are also very poor quality. Using recycled cells, very poorly welded circuits and no Battery Management System – these are just fire hazards waiting to happen.

Even worse is the DIY market. Users with little or no expertise consult on forums for guidance on making batteries at home. Often using inadequate tools and materials.


Further Reading


So what could cause an E-Bike battery to malfunction?

There is no particular answer why an eBike battery might set on fire, but in almost every case, it’s one or more of the following reasons:

Over-discharging

This is normally caused by a faulty (or not fitted at all) Battery Monitoring System (BMS). Lithium-ion cells have a DoD or ‘depth of discharge’ limit and in most cases are ‘empty’ at between 2.8 and 3.0 volts (fully charged at 4.2v). Discharging past this low voltage cut off can alter and/or damage the internal chemistry of the cell and the worse this gets and the more frequently it happens, the more the internal resistance of the cells increases over time. This makes it harder for them to expend their energy and when you then ask for more current than they can expend (or faster than they can expend), the cells heat up and this can lead to fire.

Overcharging

This happens in two ways: when a charger doesn’t shut itself off when the battery voltage reaches its uppermost level; when the BMS allows the system to be overcharged but doesn’t isolate the battery from the power supply when finished; or both. This can overheat the battery, leading in extreme cases to fire. However, it can also be from trying to charge too quickly. This is normally a result of not using the correct charger – i.e. a charger with a supply current and/or voltage higher than the battery is able to safely manage. This too leads to overheating, and subsequently fire if the BMS or charger doesn’t recognise the issue and isolate itself.

Bad quality or no BMS

As well as reducing the likelihood of the above two scenarios, the BMS itself is also a potential failure point. Bad quality ones tend to fail in the ‘on’ position. In other words, when it fails it effectively ceases to exists and allows the battery to be overcharged and over-discharged, sometimes without any real warning. Good quality BMS like those found in Bosch and Yamaha systems fail ‘off’ and are connected to the central control system of the bike. They will not only lock up the battery from being used, but will remain ‘contactable’ and when plugged into diagnostics, an authorised repair centre will be able to see exactly what has gone wrong.

Mechanical/physical damage

Good quality batteries have the ability to deal with the normal bumps, jolts and scrapes that even aggressive mountain biking brings, but none are infallible. If your battery suffers a drop or fall of more than a few feet onto a hard surface it should not be used. We advise you visually inspect your battery regularly for external damage to the casing plus giving it a gentle shake to check for rattles. 

Thermal runaway

Thermal runaway is almost always a secondary effect to one or more of the above external factors and doesn’t simply just ‘happen’. Over-charging, over-discharging, leaving the battery exposed to extreme (60C+) temperatures or severe impacts can lead to internal shorts which gradually heat the battery pack beyond safe working limits, causing the cells inside to ‘vent’. This is characterised by a popping noise, followed immediately by a hiss as a cell vents its rising internal pressure. Cells like the cheap Chinese unbranded ones often don’t have this manufactured-in weak point (a ‘burst disc’).

Here is some handy advice from the National Fire Chiefs.

  • 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 eBike 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 fault should occur you can respond quickly. Don’t leave batteries to charge while you are asleep or away from the home.
  • Charge your battery on a hard flat surface, in an area where there is adequate ventilation (not in a cupboard or under the stairs etc) 
  • 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.
  • Do not overload socket outlets or use inappropriate extension leads (use un-coiled extensions and ensure the lead is suitably rated for what you are plugging in to it).
  • If you see any damage to the charger or the battery then don’t attempt to charge it and contact a reputable retailer to obtain a replacement.
  • In the event of an eBike or any lithium-ion battery fire – do not attempt to extinguish the fire. Get out, stay out, call 999.

As a business we have sold over 15,000 electric bikes. All of them legal to ride. All of them safe to ride. Are electric bikes safe? We say 100% yes they are

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