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.