I know these are currently out of fashion but I'm still thankful they exist.
Let's remind ourselves of devices that use(d) these standardized batteries:
- Toys
- Digital cameras
- Torches
- Gadgets like fans
- Wireless keyboards
- TV remotes
Thanks to having a standardized system of batteries,
- You can use the same battery across several devices. This is a no brainer but it's very practical.
- Batteries can charge quicker thanks to being put in a dedicated charger and not being limited by USB cables. (But yes I concede that USB has been updated for faster charging over the years)
- Devices don't have down time when their battery is charging. To charge, the battery is removed from the device and can immediately be replaced with a fresh one.
- You'll never have to trash a device due to an expired battery. Just buy a replacement. And building on this...
- Any improvements in future battery technology can be retro-fitted into your existing devices. And there is a high incentive for future improvement, because...
- An accessible (due to easy replacement) and large (due to many devices) battery market is very attractive to competition.
If you look at the pros I listed, they all happen to be things that would be very useful for electric cars. So I think it would aid the adoption of electric cars if their batteries were standardized too.
While all this is true, unfortunately not many devices support swappable 18650s, either they have swappable AA/AAA or have built-in 18650s that would require disassembly to replace. However, if you CAN find a device with swappable 18650s (the only ones I've found so far are flashlights) they're absolutely great!
I am not aware of many devices that use swappable 18650's either. Off the top of my head the only ones i'm aware of are vape devices.
There are also flashlights with 18650s. There are some powerbanks with exchangeable 18650s as well.
But that’s all I know of.
I have a set of lasers powered by them as well. Love that it makes the whole thing a bit larger and durable.
These powerbanks can set your house on fire if the chip shorts out: the wire gets very hot and melts through the plastic like this: Odysee/YT/Piped. I recommend installing a 2A (for 1A powerbanks) or 5A (for 2.1A powerbanks) automobile fuse in series with the cells or each cell individually.
My OWON portable oscilloscope does. The only device I know of.
Wait, do they not make AA-sized 18650 batteries?
18650 isn’t a specific type of battery, but a size. 18mm diameter, 65mm length, and 0 typically represents it being cylindrical in shape. 18+65+0
Heres a quick read
Besides being the wrong size by definition, AA batteries are expected to have 0.8V to 1.5V, while Lithium Ion cells (such as 18650) have a voltage range of 2V to 4.2V. That’s completely incompatible, you couldn’t even replace two AA batteries with a single Li-Ion cell.
That can actually work. A single 14500 Li-Ion along with a dummy battery can work in many devices, as they have regulators for the voltage in the device (it might blow up other devices and won't give any energy advantages). That said, there is very rarely any use for this these days, as you can buy 1.5V AA Li-Ion batteries with the voltage regulator build in, that will work in all devices. More expensive than NiMH however, so only really good when the device absolutely needs the 1.5V and isn't happy with the 1.2V of NiMH.
Couldn't it theoretically be fixed with a voltage regulator?
Don't they need a circuit protection to not over-discharge lithium batteries? Most AA devices would suck all the juice from the battery until it stops working.
Yes.
The other problem with lithium batteries like 18650s is that they need to be handled with care so manufacturers don't want users swapping them in and out like AA/AAA. This is why they build them into devices and have you charge them through a regulated port.
Also there are numerous different versions and sizes of 18650, some come with protection circuit, some don't, some have flat top, some have button top, and whatever type you end up with might or might not fit your device. Makes the whole situation quite confusing for the average user.
Well there aren't really different sizes of 18650s, if you chance the size it's no longer an 18650.
The flat vs button top issue can be annoying though
18650 with protection circuit are around 69mm in length instead of 65mm.
The problem with those is that the device loses the ability to sense the charge status of the battery, since the voltage remains the same until it’s empty.
NiMH AA's have the same problem.
Most 18650's don't go down to 2 volts. They should be considered "flat" at 3.4 volts - going any lower risks damaging the battery (unless you know what chemistry it uses, some can go lower safely).
Allowing a rechargeable AA to get down to 0.8V is also risky, if you go much lower than that you will damage the battery.
An 18650 is essentially the same voltage as three AA's. And the amount of charge level they store is closer to five or six. The size and weight, on the other hand, is a bit more than one AA.
But the biggest advantage, by far, is a lot of devices can be powered by a single 18650 but would require multiple AA's to have acceptable battery life (or a high enough voltage). As soon as you have multiple batteries thing start to get really complex. Your batteries will never be at exactly the same charge state and that can potentially damage the battery and the device.
They do, they are called "14500" (the name is the dimensions of the battery). Though it is important to remember that, despite looking exactly the same as a regular AA, they are 3.7V, so they'll kill your regular 1.5V electronics if you put them in there. Not sure what they are actually used in, flashlights I assume, but they seem quite rare overall.
Only place I have seen them commonly used is solar powered garden lights, though in that case they are LiFePO4 3.2V, not Li-Ion 3.7V.
But 18650 size is manufactured at much higher scales than other sizes, and therefore it's the cheapest, and therefore it continues to dominate.
The main barrier is when you need multiple batteries.
If you install a dozen 18650's in a device (or thousands in a car), they will work great as long as they're all at the same charge level and can maintain the same voltage throughout the discharge cycle. If they can't do that, then the battery could catch fire. Yikes. So any device with multiple 18650 cells will hard wire them together so the user is forced to use and charge and discard the entire set of cells as a single battery.
AA/AAA NiMH batteries won't catch fire if they're uneven, but being uneven will damage the batteries. You don't need to keep them together to be safe, but you do need to keep them together if you want the batteries to last longer than six months. Keeping them together can be a logistical nightmare and it's the main reason I've stopped using them... it's just too much work to keep all the batteries together (especially if the device is shared in a household or workplace). If you get it wrong, then they don't last much longer than disposables.
Disposable batteries have the same issue - but since they're disposable you're probably pulling four brand new batteries from a packet.
An 19650 cell holds about the same amount of energy as five AA batteries. So there are a lot of devices that can run well off a single battery, and those tend to be the ones that are user replaceable.