Do you know of any devices that don't require a reboot when you switch batteries? It shouldn't be difficult to implement. All you have to do is build a small second internal battery into the device that could keep the volatile memory alive during the switch.

But then there's no perceived need for it for 99% of users so, like many neat things, it will unfortunately never be built into mass-produced phones because it doesn't make business sense.

That same idea is apparently there in the upcoming Thinkpad T440s laptop (3 cell internal + 3 cell swappable). I really hope it catches on in other laptops and phones - I find I often go past a typical phone & laptop's battery span without a power plug around.

Thinkpads have supported a second battery in the UltraBay for a long time, as well.

FYI, they had this feature on PDAs of yesteryears since their battery life was terrible.

[RIP my Axim X30]