c't fire test: Beware of cheap charging bags for e-bike batteries
We wanted to know: What happens if an e-bike battery burns down in a cheap charging bag that is advertised as fireproof?
Fireproof, explosion-proof - the sellers of cheap protective bags for lithium-ion batteries advertise with such attributes. A fire test by c't now shows that you should not rely on such advertising promises. In the test, a cheap charging bag failed completely. Shortly after the first battery cell exploded, flames were already shooting out of it. After the fire, only a few shreds were left.
For the test, we selected a charging bag designed for e-bike batteries, which a Chinese seller offered on Amazon.de for around 20 euros. It was advertised as "fireproof" and "explosion-proof". "The three-layer composite material is strong and reliable for maximum insulation against explosions and debris," the description read. As a fire load, we chose a new, fully charged e-bike battery with 375 watt hours - a fair opponent for the cheap bag, as there are e-bike batteries with more than 700 watt hours.
We carried out the test at the company Fisacon in Rheda-WiedenbrĂĽck. This company develops charging boxes for batteries and therefore competes with the manufacturers of charging bags, even if the Fisacon boxes are in a different segment with prices of over 1500 euros. We chose the bag and the battery ourselves, Fisacon only provided the ignition device and the fire container.
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A few minutes after switching on the glow igniter from a safe distance, the first plumes of gray smoke billowed out of the bag, and five minutes later the first battery cell exploded with a bang. Just ten seconds later, the bag was on fire, as our video shows:
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More exploding cells flew around the fire container unhindered. If the test had taken place in an apartment, the battery would not only have set fire to furniture in the immediate vicinity, but probably also to flammable objects a few meters away.
We don't want to spread panic: Measured against the number of rechargeable batteries sold, fire incidents are very rare and much rarer still with externally intact rechargeable batteries.
Expert: Bags can do more harm than good
However, a bad bag can do more harm than good in an emergency. "The heat is concentrated in a pocket, which makes the chain reaction of the battery more likely and even accelerates it," said battery expert Sascha Bruns from the Gesellschaft fĂĽr WerkstoffprĂĽfung (GWP), who has carried out numerous fire tests himself, to c't. If several cells explode as a result, the battery could tear or burn the bag and the result could ultimately be worse than without a container.
Bruns emphasized that, in principle, a bag does not prevent flammable, harmful gases from escaping from it. This is because when the electrolyte vaporizes, its volume increases many times over. With bad luck, the gases then also ignite outside the bag, leading to a dangerous deflagration. This is another reason why it is important to store batteries in a room with as little fire load as possible, possibly under an open window or in a sufficiently cool place outdoors.
Similar bags are still available
We informed Amazon of the results of our exemplary fire test and pointed out that, in our opinion, most bag models in the same price range offer similarly poor protection against fires. The company removed the bag model we tested from the platform. "We have removed the product in question for the duration of the investigation," said a spokesperson. In general, the company "proactively removes products in the event of product safety concerns". However, many apparently similar models can still be found on Amazon.de. Many of these bags are also advertised by the sellers as "fireproof" and "explosion-proof".
Read more on this topic at c't:
- Battery fires: between scaremongering and facts
- Why a battery burns and how you can prevent it
- Battery cases and boxes: Exemplary fire test and market overview
(cwo)
