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.
Wait, do they not make AA-sized 18650 batteries?
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.
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.
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.