Instead of a hot-swappable battery, why not just carry a large battery-bank that can charge your laptop over USB-C? That way you don't even need to reboot.

Browsing around on Amazon, I see there's actually quite a few battery banks that with over 60W of output, and ~100Wh of capacity for under 100€

I assume for the same reason some people like integrated WWAN modems, it's annoying to have a device dangling off the side