E-bike Battery Safety and Longevity

Battery care

We are often asked the best way to charge batteries to get the best life out of them. Less often is the average e-bike user aware of the potential fire dangers of e-bike batteries.

Happily, the strategies that will maximise battery longevity will mostly minimise risk of fires, as both revolve around minimising the stress that the battery experiences during its life.

Below are my thoughts on how to best take care of your battery in a practical sense for real world e-bike owners. I’ve never been comfortable with throw-away lines like ‘always supervise your battery while charging’ – they just aren’t practical for actual people in real lives and simply move the liability to the consumer. And because no-one can picture anybody actively watching their battery charge, they then assume that there is no need to think about battery safety at all.

Please send us your feedback about what you think of the tips below and what you have tried in your daily life

Battery Safety Manual – by Maurice Wells, first published in 2019 on glowwormbicycles.com.au. Revised here in 2021

The safety of both our customers and their possessions is important to us. The batteries in the e-bikes we sell are lithium-ion batteries, built with the latest technology, compliant to relevant safety standards. When charged, lithium-ion batteries contain a high level of energy. If a fault occurs internally (not visible) or externally, a lithium ion battery can catch fire. It is not often possible to know beforehand whether your battery is a higher than normal fire risk.

Therefore it is very important to minimise both the risk of this occurrence through proper battery care, as well as minimising any potential consequences, through best charging practices.

The information below is generic and may be useful for any lithium battery you own. Please keep in mind though, the context of it is based around the batteries that we have experience in selling – typically eZee, Bosch and Shimano batteries. Bosch has its own battery manual, as does Shimano.

The information included here was created with forethought and care. However, we can not guarantee that all information within is completely accurate or error free. No liability can be accepted for damages which come about either directly or indirectly from suggestions in this post, so far as there is no deliberate intention or gross negligence from the author or publisher.

1 – Battery Care

– Protect the battery against physical stress. Keep away from:

• excessive exposure to direct sunlight (eg daily storage of battery or bike in a window facing the sun)
• direct heat sources such as home heaters or fires
• submersion in water
• physical damage (dropping)

– Take care of the battery from physical damage. Do not allow it to be dropped, carelessly transported (eg in a backpack without proper protection, or sliding around in the boot of your car). If your bike has a serious crash, return to your shop for inspection of bike and battery. If you can, avoid removing your battery on a daily basis (eg by changing where you charge).

– Keep your battery away from any small metal objects when the battery is not installed into the bike. Small tools, scrap cabling, paper clips etccould short circuit the battery terminals.

– Do not open the battery. This voids the warranty and may increase risk of fire.

– Keep the battery away from children. They love seeing all the ways they might be able to charge it.

– Understand that your battery will not last forever. There will come a day when it needs replacing. The visual exterior condition, its functional capacity (how far you can ride on it compared to when it was new) and its age are all factors. Experience has shown us a typical result for a regular user is around 5 years before a battery needs replacing. Continuing to use a failing battery can increase risks as it is getting older and less predictable and under more stress. When you do eventually purchase a new battery, return your old one to your supplier for safe recycling. Keeping your old one as a ‘spare’ around your house is an unnecessary risk for very little gain.

2 – Charging Best Practice

Unfortunately the default practice of plugging the bike in when you get home and letting it charge all night while you sleep is not the safest method. There are two well documented battery fire cases in Sydney homes where the owner’s did just that. These cases help to illustrate what is at stake and also to help you imagine the situation if your battery were to ignite inside your house: 1 – Melanie Sandford in leichhardt, 2019, 2 – Darlinghurst house fire, 2021.

Lithium batteries are at their highest level of stress when at full charge. This includes when the battery has finished charging, even if disconnected from the charger. The tips below will not only minimise the chance of any adverse incident, but they will also help to increase the longevity of your battery. The tips below are to help you assess the best charging practice for your usage patterns and home situation. Not all scenarios below are workable for all people (indeed some contradict each other), so it’s up to you to decide what works best for you and accept the risks you are taking.

2.1 Charging Regime – Minimise how many hours per week your battery is at a full state of charge. Depending on your situation, this could be done by:

• charging every few days instead of every day
• program a power point timer so that your battery begins charging at dawn and has charged sufficiently when you’re ready to leave the house on your e-bike. The ideal is if it’s not quite fully charged when you leave.
• For a shared or fleet e-bike situation, instruct users to put the bike on charge only when it reaches half full, as opposed to every time a short ride is taken
• for irregular users (eg holiday homes), do not leave your battery on a timer to occasionally ‘top up’ the battery. This is unnecessary and keeps the battery at a high state of stress more or less 24/7.

If you are about to stop using your battery for a period of time, leave it at about ¾ of a full charge, as this is the most stable state of charge, increasing longevity and reducing risks. High quality e-bike batteries (eZee, Bosch, Shimano etc) do not suffer ‘self-discharge’, so they do not need ‘topping up’, even if left for months.

2.2 Charging Location – Choose the safest charging location on your property. This may involve creating a suitable space through installation of a power point (or safely running an extension cord), building an outdoor awning/shelter or shifting around a garage layout. Not all home situations are the same and your own daily patterns will also influence where is the best place and time to charge. Some situations are inherently safer, such as outside the house, but are more difficult to supervise. It’s up to you to assess the risks and make a decision for what works best in your space and life style.

• Make sure your home is fire safe, regardless of your ownership of an e-bike. This means (hard wired) smoke alarms and not ‘dead locking’ your doors. Refer to the fire service for more tips
• do not charge your battery underneath curtains, in a cluttered area, near solvents and paints or directly between you and your exit from your house.
• Is there a suitable place you can charge that is not inside the home, but still protected from weather (eg carport or back porch)? If so, this is probably the best place to charge your bike. It is probably worth the effort to install a power point or organise a cord in that area.
• Is there an outdoor place that would be suitable if it had shelter or protection from theft? Considering having it built to suit! E-bikes have already revolutionised your life, make it permanent!
• Leaving the battery in the bike while charging is ideal if you can. It reduces occurences of dropping the battery and the bike’s frame is metal and keeps the battery some distance away from other materials.
• If you must charge your battery off the bike and inside your home, where can you charge that has the best ventilation (next to an open window) and the fewest flammable materials around? This may be in the laundry, the fire place (obviously when not being used for a fire!) or a kitchen bench. You may want to buy a large metal container (fire box) to charge in, with a lid that you can close shut if the battery ignites.
• The charger should always be on a clean, dry, flat and fire-proof surface, as the charger does create heat while charging.

Remember, even if you’re awake, you cannot rely on your ability to move the battery or do anything other than run away (read Melanie Sandford’s description of events here). Wherever you plug the battery in is likely where it will stay if it catches fire. So in that position, ask yourself what would happen if it caught on fire. Would anyone be hurt? Would the house burn down? If you answer that the house would quickly catch alight while you sleep and you’d struggle to exit it, then you need a better charging strategy! Feel free to contact us for ideas.

3 – Fighting the Fire

As mentioned above, you cannot count on your ability to do anything other than just run away in the moment. But let’s suppose that you are safely able to attempt to put the fire out. The first step would be to move the battery somewhere safer (outside) where you can just abandon it and leave at any moment. This is likely only to be possible if it hasn’t yet completely ignited (smouldering) or you had been charging it in a metal box or something that allows you to move the battery without touching it. Next comes trying to put it out.

The transport industry knows a lot about the risks of lithium battery fires and this industry article is worth a read. The quick takeaway is that “Lithium ion batteries are a Class B flammable liquid and require dry chemical extinguishers to put out”. So if you’ve got one of those handy, then go for it, as long as you’re able to stay safe.

The article goes on to say that (contrary to popular belief), water can put out a lithium battery fire, if you don’t have a dry chemical extinguisher. The strategy here is to cool the battery cells down with the water. Your best chance at this is if the battery were inside a container that you can fill up with water, eg in a metal box you use for charging. Or in a bucket outside that you managed to drop the battery into, then fill up with a hose. If the battery is not contained in anything, then you don’t have a good chance of cooling it sufficiently with a hose. But if you’re safe and outside and waiting for the fire truck, you may as well give it as much water as possible. Here is a video that has done the rounds on someone doing just that. As this person caused his own fire (shorted the battery via a faulty controllor), he was able to witness it from the start where it is smouldering. You won’t be so lucky if the fire starts while you are not present! The comments on his video suggest that he was making it worse with the water. This is incorrect, he was at least cooling the cells down what little he could. The only other thing he may have been able to do better is put the phone down, get a hammer, break the battery case open so that he could pour water directly on the cells. That and moving the bike further from the house perhaps!

After the fire has been put out, the job is not done! At any moment the fire can start again. The fire fighters may not be aware of that, so you might ask them to dispose of the battery for you. Or if you’ve put it out yourself, put it somewhere safe so that if it catches again, it won’t harm anyone or spread.