@parker @charlie_root @gabriel @fcgreg you can also design batteries to be backpackable -- a slim on that fits in the case, a fat one that covers the back of the case and expands the volume for power cells.
There's no reason batteries have to have any particular form, so give or take the latching, sliding, or covering hardware and enclosures I don't imagine it would be a significant difference, but it's definitely something to watch for in specs. If it adds 2mm to the mobile's thickness... 🤷♂️