Just don’t buy any extremely cheap powerbanks unless you know how to inspect and test them.
The issue is not only about the number of cells, but it’s also about the construction of the charger. Obviously, more poorly managed cells can create more of a problem, but most lithium batteries die violently when damaged, regardless of size. (Lithium batteries are so common now, it’s easy to forget that they can be dangerous. Their construction is generally better these days, but that alone doesn’t mitigate all risk.)
Unfortunately, powerbanks are usually sealed so they are hard to open and inspect. If you do get them open, you need to understand what you are looking for, which can be challenging. There is also a risk of damaging a cell when you open them, which is also bad.
Name brand chargers simply give you someone to sue. (Random knock-off brands don’t.) Because of the liability, name brands usually have better construction and go through some kind of safety testing. Edit: The batteries don’t need to be “name brand”. If you bought a random powerbank at a reputable store, the store itself may assume the liability. (Large stores can distribute name brand products under a house name, in some cases.)
Wiring problems, mismatched cells without protection and poorly designed charging circuits are usually the issues.
Lithium batteries can catastrophically fail for a number of reasons. Internal shorts from discharging too low, external shorts, over charging, over discharging, physical damage, and heat to name a few.
If your charging circuit isn’t balance charging the cells properly or the overcharge protection fails, then it can cause many of those issues to happen much faster.
Moral of the story: never leave a charging battery unattended.
Just don’t buy any extremely cheap powerbanks unless you know how to inspect and test them.
The issue is not only about the number of cells, but it’s also about the construction of the charger. Obviously, more poorly managed cells can create more of a problem, but most lithium batteries die violently when damaged, regardless of size. (Lithium batteries are so common now, it’s easy to forget that they can be dangerous. Their construction is generally better these days, but that alone doesn’t mitigate all risk.)
Unfortunately, powerbanks are usually sealed so they are hard to open and inspect. If you do get them open, you need to understand what you are looking for, which can be challenging. There is also a risk of damaging a cell when you open them, which is also bad.
Name brand chargers simply give you someone to sue. (Random knock-off brands don’t.) Because of the liability, name brands usually have better construction and go through some kind of safety testing. Edit: The batteries don’t need to be “name brand”. If you bought a random powerbank at a reputable store, the store itself may assume the liability. (Large stores can distribute name brand products under a house name, in some cases.)
Wiring problems, mismatched cells without protection and poorly designed charging circuits are usually the issues.
Bonus! bigclive doing some destructive testing on batteries: https://youtu.be/EgtKwxzgggg
Lithium batteries can catastrophically fail for a number of reasons. Internal shorts from discharging too low, external shorts, over charging, over discharging, physical damage, and heat to name a few.
If your charging circuit isn’t balance charging the cells properly or the overcharge protection fails, then it can cause many of those issues to happen much faster.
Moral of the story: never leave a charging battery unattended.