Honestly the issue is that schools don't want calculators (computers) that are too powerful because there could be an app that can just do the homework for students, or let them communicate during exams, or search on the internet. So schools intentionally prefer crippled devices, hence the relatively high price for an underpowered device.

There's not really any good solution to this either without completely overhauling the system (i.e. making things worse for a few years until things stabalize and the kinks are worked out in primary school math education 2.0), so we're at a local maximum.

I don't get your point about batteries though. Calculators are heavily used by the students, so are the perfect place to have a rechargeable. It looks like it's even replaceable too. Throw in usb-c charging, and you've got something that can be charged pretty much anywhere that a phone can.