I thought the argument against this was that then you lost volume to the casing, connector, removable cover, etc. which could be better used by a funny-shaped collection of various-sized batteries.

Battery swap requires a reboot (usually) which is bit annoying.

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]

LOTS of phones allow a battery swap. As far as I know the only phone that doesn't is the iPhone.

Nexus 4 doesn't have an easily replaceable battery either.

Sony Xperia S, probably others. Plenty of phones have non user replaceable batteries.

New nokias don't.

iPhone, Nexus 4, and HTC One

Moto X

Wouldn't try it with the HTC One X

But if you swap batteries, then when you get to an outlet, you either need a special charger for the spare battery, or you need to swap batteries while charging.

the main reason to have spare batteries for me at least is to keep the spare batteries charged up and ready to roll. But yes this does require a specific battery charger. when i had my HTC Thunderbolt, i got a package deal with 2 batteries and a charger ( that also provided a USB port ) for < $20. I haven't looked for my S3 yet...