> RaspberryPies and such are commodity hardware. You can buy one, two, ten, twenty, a hundred, and it just scales along.

Not my experience at all. Pies are hard to find, get more expensive each week. Some are impossible to find (Pi zero).

The most fragile part of a phone is the screen. If you don't care about breaking it, then access to the battery becomes pretty easy, and therefore easy to replace.

Same here. The last times I tried to get a Pi — three times in three years — the ones I wanted were completely sold out and waiting to restock.

Where are you based? I just bought 25 from CPC without any issues. Delivered in two days. They aren't as cheap as they used to be, but I understand the reasons why, given how expensive RAM is. Yes, the zero is trickier, but the 2W is in stock on PiHut at the moment.

It seems very regionally dependent.

I think battery replacement is only part of the problem, though. Even if you can swap batteries cheaply, you're still dealing with different firmware versions, component revisions