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.
Those batteries in your photo are NiMH batteries... which discharge on their own at a fairly rapid rate even if you're not using them at all. They're also pretty big and heavy for the amount of power they provide (which, due to the self-discharge issue, is effectively a lot lower than the official number on the battery).
I strongly recommend investing in devices that use 18650 batteries. They're about the same size/weight as a AA, and they last much longer (both in terms of from full to flat and also the number of years (decades?) of use you'll get from the battery.
A lot of "proprietary" batteries are in fact a bunch of 18650 cells wired together.
It's worth investing in good ones - the quality varies significantly from brand to the next. With a good 18650 cell, you won't be replacing it when the battery expires, you'll be transferring it to a new gadget when the gadget is broken or so old that you decided to buy a new/better model.
They make USB rechargeable lithium ion batteries in every common form factor. I use lithium rechargeable AAA batteries in my mouse and they work great. You don't even need a charger, they are USB-C. Highly recommend.
They can be very useful for the devices that want the full 1.5V, as they can provide that 1.5V across their whole charge cycle, unlike NiMH and Alkalines that drop down the voltage. They are also lighter than NiMH. However they are also more expensive and for most devices NiMH will work just as well, while costing less.
Another thing worth mentioning, NiMH show charge in mAh on the package, Li-Ion very often give it at mWh, which makes the Li-Ion look 20% bigger than they are.
I mean I can't really blame them for being smaller, the USB port is a lot of value added but is also pretty huge.