Im in Germany and haven't had a leaking battery (except the ones that come with cheap chinese electronics). And I mostly buy the cheap batteries from the supermarket. I just don't buy batteries, that weight nothing.
If you give away the card to your kid just leave your switch in airplane mode and you won't have a problem. But even so it's not allowed to do that. Btw you can also do that with a digital copy to lend it to another switch while in airplane mode.
I mean that really depends on the country, but I was talking how that usually is in my experience. In Germany you have to own the original medium of a backup and according to a quick google search same for the US.
Its legal as long as you don't sell the original game. And as long as you don't do that there isn't a problem either. The issue stems from copying a game, selling the original and still use the copy. If no 2 copies of the same cartridge are online at the same time then there is no issue.
Im treating them as too lazy and not willing and not as too stupid. And both lazyness and not willing to put in extra effort are completely valid reasons to not do something.
Basically he tests a variety of brands and alkaline vs lithium in various ways. And towards the end of the video at 19:42 and 19:50 there is a graph and table with the results.
Just take 2 circles and do the same the resulting image will also have a perfectly straight line.