[mikeash]

I don't think you really need a source for this. Current smartphone batteries last about a day in normal use. If you made it seven times larger, it would still be portable (just less so), and would now last a week. Increasing battery capacity by just adding more battery is trivial. What's hard is adding capacity without adding bulk or cost.

[olla]

Yes, bulk is quite important factor too, especially on storing energy on large scale. Agreeing with the "can do a week of battery phone" on the other hand depends. The problem is that smart-phones have achieved lately their acceptable speeds with quad core (and up) processors. Resolution of screen makes less impact than the mere size of the area that has to be lit, but nobody wants to surf web through a peephole. E-ink would rescue if it could play videos and games fast. A lot of people want to do exactly that. And there are a lot of additional features we are used to keeping active (gps, wifi, ...). Turning these off will decrease the value of having a smartphone. Based on current battery sizes a week of battery would probably mean about 5 times the battery of phones now. That is not pocketable computer territory anymore.

In addition I would really like to have the phone component moved to watches (with at least 3 days battery) and leave all the rest for a pocketable computer to handle.

[MichaelGG]

The Huawei Mate 2 has a 4000mah battery and I regularly get two days (30-40 hours) on it. It's very handy never having to worry about charging. It's thin and light (cheap feeling). As much at it sucks from crappy software (messed up version of Jelly Bean) and as much as I want to leave Google, no one else seems to be targeting even 20 hours of life. It's very frustrating.

The Mate 2 feels small enough that doubling the thickness would still result in an acceptable phone.