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.
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.