Yeah, the last troublesome Apple laptops I had to deal with were 2001-era iBooks. Those were kinda tricky.
" Maybe batteries have to be sold with a hard shell, the MacBook Pro battery doesn’t have that in order to save space"
And the saved space can either be used for more battery, or to reduce the size of the computer. They save the thickness of the battery case, and the thickness of any internal walls in the battery compartment with which a removable battery would mate. I'd think those walls might need to be somewhat substantial, to keep the battery in and prevent flexing and loose connections.
I suppose in theory they could also use irregularly-shaped batteries, that would let them fill every bit of space with battery.
" Maybe batteries have to be sold with a hard shell, the MacBook Pro battery doesn’t have that in order to save space"
And the saved space can either be used for more battery, or to reduce the size of the computer. They save the thickness of the battery case, and the thickness of any internal walls in the battery compartment with which a removable battery would mate. I'd think those walls might need to be somewhat substantial, to keep the battery in and prevent flexing and loose connections.
I suppose in theory they could also use irregularly-shaped batteries, that would let them fill every bit of space with battery.